MP Materials (MP) 10-Q 13 May 21 2021 Q1 Quarterly report Financial data

COVER

COVER - shares	3 Months Ended
	Mar. 31, 2021	May 01, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-39277
Entity Registrant Name	MP Materials Corp. / DE
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	84-4465489
Entity Address, Address Line One	6720 Via Austi Parkway, Suite 450
Entity Address, City or Town	Las Vegas
Entity Address, State or Province	NV
Entity Address, Postal Zip Code	89119
City Area Code	702
Local Phone Number	844-6111
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		170,745,813
Amendment Flag	false
Entity Central Index Key	0001801368
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Current Fiscal Year End Date	--12-31
Common Stock, par value of $0.0001 per share
Document Information [Line Items]
Title of 12(b) Security	Common Stock, par value of $0.0001 per share
Trading Symbol	MP
Security Exchange Name	NYSE
Warrants to purchase Common Stock
Document Information [Line Items]
Title of 12(b) Security	Warrants to purchase Common Stock
Trading Symbol	MPWS
Security Exchange Name	NYSE

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 1,181,515	$ 519,652
Accounts receivable (including related party), net of allowance for credit losses of $0 and $0, respectively	13,925	3,589
Inventories	35,098	32,272
Prepaid expenses and other current assets	8,583	5,534
Total current assets	1,239,121	561,047
Non-current assets
Restricted cash	9,115	9,100
Property, plant and equipment, net	532,504	501,974
Finance lease right-of-use assets	974	1,028
Other non-current assets	812	1,139
Total non-current assets	543,405	513,241
Total assets	1,782,526	1,074,288
Current liabilities
Accounts payable and accrued liabilities	27,500	16,159
Current installments of long-term debt	3,105	2,403
Current installments of long-term debt—related party	38,457	22,070
Current portion of finance lease liabilities	279	266
Other current liabilities	3,580	2,163
Total current liabilities	72,921	43,061
Non-current liabilities
Asset retirement obligations	25,859	25,570
Environmental obligations	16,679	16,602
Long-term debt, net of current portion	672,582	961
Long-term debt—related party, net of current portion	17,733	44,380
Finance lease liabilities, net of current portion	687	736
Deferred income taxes	91,635	87,473
Other non-current liabilities	9,273	1,628
Total non-current liabilities	834,448	177,350
Total liabilities	907,369	220,411
Commitments and contingencies
Stockholders’ equity:
Preferred stock ($0.0001 par value, 50,000,000 shares authorized, none issued and outstanding in either period)	0	0
Common stock ($0.0001 par value, 450,000,000 shares authorized, 170,745,864 and 170,719,979 shares issued and outstanding, as of March 31, 2021, and December 31, 2020, respectively)	17	17
Additional paid-in capital	921,643	916,482
Accumulated deficit	(46,503)	(62,622)
Total stockholders’ equity	875,157	853,877
Total liabilities and stockholders’ equity	$ 1,782,526	$ 1,074,288

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Allowance for credit losses	$ 0	$ 0
Preferred stock, par value (usd per share)	$ 0.0001	$ 0.0001
Preferred stock, authorized (shares)	50,000,000	50,000,000
Preferred stock, issued (shares)	0	0
Preferred shares, outstanding (shares)	0	0
Common stock, par value (usd per share)	$ 0.0001	$ 0.0001
Common stock, authorized (shares)	450,000,000	450,000,000
Common stock, outstanding (shares)	170,745,864	170,719,979
Common stock, issued (shares)	170,745,864	170,719,979

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Product sales (including related party)	$ 59,971	$ 20,719
Operating costs and expenses:
Cost of sales (including related party)(excluding depreciation, depletion and amortization)	17,936	12,667
Royalty expense to SNR	0	487
General and administrative	13,583	3,084
Depreciation, depletion and amortization	6,150	1,271
Accretion of asset retirement and environmental obligations	593	564
Total operating costs and expenses	38,262	18,073
Operating income	21,709	2,646
Other income, net	55	82
Interest expense, net	(1,154)	(803)
Income before income taxes	20,610	1,925
Income tax expense	(4,491)	0
Net income	$ 16,119	$ 1,925
Earnings per share:
Basic (in USD per share)	$ 0.10	$ 0.03
Diluted (in USD per share)	$ 0.09	$ 0.03
Weighted-average shares outstanding:
Basic (in shares)	168,922,566	66,556,975
Diluted (in shares)	179,319,489	66,556,975

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance (shares) at Dec. 31, 2019		0	66,556,975
Beginning balance at Dec. 31, 2019	$ (18,022)	$ 0	$ 7	$ 22,768	$ (40,797)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,925				1,925
Ending balance (shares) at Mar. 31, 2020		0	66,556,975
Ending balance at Mar. 31, 2020	(16,097)	$ 0	$ 7	22,768	(38,872)
Beginning balance (shares) at Dec. 31, 2020		0	170,719,979
Beginning balance at Dec. 31, 2020	853,877	$ 0	$ 17	916,482	(62,622)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (shares)			36,320
Stock-based compensation	5,673			5,673
Shares used to settle payroll tax withholding (shares)			(10,435)
Shares used to settle payroll tax withholding	(334)			(334)
Net income	16,119				16,119
Other	(178)			(178)
Ending balance (shares) at Mar. 31, 2021		0	170,745,864
Ending balance at Mar. 31, 2021	$ 875,157	$ 0	$ 17	$ 921,643	$ (46,503)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net income	$ 16,119	$ 1,925
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	6,150	1,271
Accretion of asset retirement and environmental obligations	593	564
Gain on sale or disposal of long-lived assets	(133)	0
Stock-based compensation expense	5,673	0
Accretion of debt discount and issuance costs	1,064	239
Revenue recognized in exchange for debt principal reduction	(11,276)	0
Deferred income taxes	4,162	0
Decrease (increase) in operating assets:
Accounts receivable (including related party)	(10,336)	(41)
Inventories	(2,826)	(3,860)
Prepaid expenses, other current and non-current assets	(2,231)	(162)
Increase (decrease) in operating liabilities:
Accounts payable and accrued liabilities	3,058	(908)
Accrued interest	16	408
Deferred revenue from related party	0	4,521
Other current and non-current liabilities	(698)	(223)
Net cash provided by operating activities	9,335	3,734
Investing activities:
Additions of property, plant and equipment	(19,298)	(618)
Proceeds from sale of property, plant and equipment	125	0
Net cash used in investing activities	(19,173)	(618)
Financing activities:
Proceeds from issuance of long-term debt	690,000	0
Principal payments on debt obligations and finance leases	(276)	(210)
Payment of debt issuance costs	(17,419)	0
Other	(512)	0
Net cash provided by (used in) financing activities	671,793	(210)
Net change in cash, cash equivalents and restricted cash	661,955	2,906
Cash, cash equivalents and restricted cash beginning balance	532,440	29,572
Cash, cash equivalents and restricted cash ending balance	1,194,395	32,478
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	1,181,515	5,378
Restricted cash, current	3,765	34
Restricted cash, non-current	$ 9,115	$ 27,066

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION Description of Business: We own and operate the Mountain Pass Rare Earth Mine and Processing Facility (“Mountain Pass”), which is the only rare earth mining and processing site of scale in the Western Hemisphere. Our wholly-owned subsidiary, MP Mine Operations LLC, a Delaware limited liability company (“MPMO”), acquired the Mountain Pass mine and processing facilities in July 2017. Our wholly-owned subsidiary, Secure Natural Resources LLC, a Delaware limited liability company (“SNR”), holds the mineral rights to the Mountain Pass mine and surrounding areas as well as intellectual property rights related to the processing and development of rare earth minerals. The mine achieved commercial operations in July 2019 and we are currently working to restore the remainder of the facility for use in processing separated rare earth products. The Company is headquartered in Las Vegas, Nevada. References herein to the “Company,” “we,” “our,” and “us,” refer to MP Materials Corp. and its subsidiaries. The Business Combination (as defined below) was consummated on November 17, 2020, pursuant to the terms of a merger agreement entered into on July 15, 2020 (the “Merger Agreement”). Pursuant to the Merger Agreement, MPMO and SNR were combined with Fortress Value Acquisition Corp., a special purpose acquisition company (“FVAC”) (the “Business Combination”), and became indirect wholly-owned subsidiaries of FVAC, which was in turn renamed MP Materials Corp. The Business Combination was accounted for as a reverse recapitalization, with no goodwill or other intangible assets recorded, and the acquisition of SNR (the “SNR Mineral Rights Acquisition”) was treated as an asset acquisition. Furthermore, MPMO was deemed to be the accounting acquirer and FVAC the accounting acquiree, which, for financial reporting purposes, results in MPMO’s historical financial information becoming that of the Company. In May 2017, the Company entered into a set of commercial arrangements with Shenghe Resources (Singapore) International Trading Pte. Ltd. (“Shenghe”), a majority owned subsidiary of Leshan Shenghe Rare Earth Co., Ltd. (“Leshan Shenghe”) whose ultimate parent is Shenghe Resources Holding Co., Ltd., a leading global rare earth company listed on the Shanghai Stock Exchange, to fund the Company’s operations, identify operational efficiencies, and sell products to Shenghe and third parties. Shenghe has significant knowledge of the mining, processing, marketing and distribution of rare earth products, as well as access to customers in the Chinese market for these products. As part of these arrangements, Shenghe (and its controlled affiliates) became both the principal customer and a related party when Leshan Shenghe obtained a preferred interest in the Company, which was ultimately exchanged for shares of the Company’s common stock with a par value of $0.0001 per share (“Common Stock”) in connection with the Business Combination. See also Note 3, “Relationship and Agreements with Shenghe,” for additional information. Operating segments are defined as components of an enterprise about which separate financial information is available and evaluated regularly by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company’s chief operating decision maker views the Company’s operations and manages the business as one reportable segment. The cash flows and profitability of the Company’s operations are significantly affected by the market price of rare earth products. The prices of rare earth products are affected by numerous factors beyond the Company’s control. The products of the Company are sold globally, with a primary focus in the Asian market due to the refining capabilities of the region. Rare earth products are critical inputs in hundreds of existing and emerging clean-tech applications including electric vehicles and wind turbines as well as drones and defense applications. Basis of Presentation: The unaudited Condensed Consolidated Financial Statements of the Company have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) for interim financial information and with the rules and regulations of the U.S. Securities and Exchange Commission. Accordingly, they do not include all of the information and notes required by GAAP for complete consolidated financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included. Results of operations and cash flows for the interim periods presented herein are not necessarily indicative of the results that would be achieved during a full year of operations or in future periods. These unaudited Condensed Consolidated Financial Statements and notes thereto should be read in conjunction with the Consolidated Financial Statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
SIGNIFICANT ACCOUNTING POLICIES	SIGNIFICANT ACCOUNTING POLICIES Principles of Consolidation: The unaudited Condensed Consolidated Financial Statements include the accounts of MP Materials Corp. and its subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Concentration of Risk: As of March 31, 2021, Shenghe accounted for more than 90% of product sales. Shenghe, a related party of the Company, has entered into an arrangement to purchase substantially all of the Company’s production, and has previously purchased portions of the Company’s stockpile inventory. While as with any contract there is risk of nonperformance, we do not believe that it is reasonably possible that the agreement will be terminated in the near term as it would significantly delay Shenghe’s recovery of non-interest-bearing advance payments that are recognized by the Company as debt. See Note 3, “Relationship and Agreements with Shenghe,” for additional information. Furthermore, while revenue is generated in the United States, our principal customer is located in China and may transport and sell products in the Chinese market; therefore, the Company’s gross profit is affected by Shenghe’s ultimate realized prices in China. In addition, there is an ongoing economic conflict between China and the United States that has resulted in tariffs and trade barriers that may negatively affect the Company’s business and results of operations. In December 2019, a novel strain of coronavirus (known as “COVID-19”) began to impact the population of China, where our principal customer is located. The outbreak of COVID-19 has grown both in the United States and globally, and related government and private sector responsive actions have adversely affected the global economy, including significant business and supply chain disruption as well as broad-based changes in supply and demand. In December 2019, a series of emergency quarantine measures taken by the Chinese government disrupted domestic business activities in China during the weeks after the initial outbreak of COVID-19. These disruptions have occurred periodically since the start of COVID-19 outbreak as measures intended to impede the spread of the virus have adapted. Since the initial COVID-19 outbreak, many countries, including the United States, have imposed restrictions on travel to and from China and elsewhere, as well as general movement restrictions, business closures and other measures imposed to slow the spread of COVID-19. At the onset of the outbreak, we initially experienced shipping delays due to overseas port slowdowns and container shortages, but we did not experience a reduction in production or sales. However, beginning in the fourth quarter of 2020 and continuing into the first quarter of 2021, we again saw shipping delays and container shortages from congestion at port facilities, which has been exacerbated by COVID-19. Congestion at U.S. and international ports could affect the capacity at ports to receive deliveries of products or the loading of shipments onto vessels. As the situation continues to develop, it is impossible to predict the effect and ultimate impact of the COVID-19 pandemic on the Company’s business and results of operations. While the quarantine, social distancing and other regulatory measures instituted or recommended in response to COVID-19 are expected to be temporary, the duration of the business disruptions, and related financial impact, cannot be estimated at this time. Use of Estimates : The preparation of the unaudited Condensed Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect (i) the reported amounts of assets and liabilities, (ii) the disclosure of contingent assets and liabilities at the date of the unaudited Condensed Consolidated Financial Statements, and (iii) the reported amounts of revenues and expenses during the reporting period. Accordingly, actual results may differ from those estimates. Debt Issuance Costs: Debt issuance costs that are incurred by the Company in connection with the issuance of debt are deferred and amortized to interest expense using the effective interest method over the contractual term of the underlying indebtedness. Debt issuance costs reduce the carrying amount of the associated debt. Recently Issued Accounting Pronouncements: As an “emerging growth company,” the Jumpstart Our Business Startups Act (“JOBS Act”) allows the Company to delay adoption of new or revised accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. The Company has elected to use this extended transition period under the JOBS Act. The adoption dates discussed below reflect this election. In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurements of Credit Losses on Financial Instruments” (“ASU 2016-13”), which sets forth a “current expected credit loss” model which requires the Company to measure all expected credit losses for financial instruments held at the reporting date based on historical experience, current conditions, and reasonable supportable forecasts. We elected to early adopt ASU 2016-13 during the first quarter of 2021 using a modified retrospective approach, which did not have a material impact on our unaudited Condensed Consolidated Financial Statements, and did not result in a cumulative-effect adjustment. In August 2018, the FASB issued ASU No. 2018-15, “Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract” (“ASU 2018-15”), which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ASU 2018-15 requires capitalized costs to be amortized on a straight-line basis generally over the term of the arrangement, and the financial statement presentation for these capitalized costs would be the same as that of the fees related to the hosting arrangements. We elected to early adopt ASU 2018-15 during the first quarter of 2021 using a prospective approach, which did not have a material impact on our unaudited Condensed Consolidated Financial Statements. In August 2020, the FASB issued ASU No. 2020-06, “Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity” (“ASU 2020-06”), which (i) simplifies the accounting for convertible debt instruments and convertible preferred stock by removing the existing guidance in Accounting Standards Codification (“ASC”) Subtopic 470-20, “Debt—Debt with Conversion and Other Options,” that requires entities to account for beneficial conversion features and cash conversion features in equity, separately from the host convertible debt or preferred stock; (ii) revises the scope exception from derivative accounting in ASC Subtopic 815-40, “Derivatives and Hedging—Contracts in Entity’s Own Equity,” for freestanding financial instruments and embedded features that are both indexed to the issuer’s own stock and classified in stockholders’ equity, by removing certain criteria required for equity classification; and (iii) revises the guidance in ASC Topic 260, “Earnings Per Share,” to require entities to calculate diluted earnings per share (“EPS”) for convertible instruments by using the if-converted method. In addition, entities must presume share settlement for purposes of calculating diluted EPS when an instrument may be settled in cash or shares. We elected to early adopt ASU 2020-06 during the first quarter of 2021 using a prospective approach. See Note 8, “Debt Obligations,” for a discussion of our Convertible Notes (as defined in Note 8, “Debt Obligations” ), which we issued on March 26, 2021. A variety of proposed or otherwise potential accounting standards are currently being studied by standard-setting organizations and certain regulatory agencies. Because of the tentative and preliminary nature of such proposed standards, we have not yet determined the effect, if any, that the implementation of such proposed standards would have on our unaudited Condensed Consolidated Financial Statements.

RELATIONSHIP AND AGREEMENTS WIT

RELATIONSHIP AND AGREEMENTS WITH SHENGHE	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
RELATIONSHIP AND AGREEMENTS WITH SHENGHE	RELATIONSHIP AND AGREEMENTS WITH SHENGHE Original Commercial Agreements In May 2017, prior to our acquisition of the Mountain Pass facility, we entered into a set of commercial arrangements with Shenghe, which principally consisted of a technical services agreement (the “TSA”), an offtake agreement (the “Original Offtake Agreement”), and a distribution and marketing agreement (the “DMA”). The Original Offtake Agreement required Shenghe to advance us an initial $50.0 million (the “Initial Prepayment Amount”) to fund the restart of operations at the mine and the TSA required Shenghe to fund any additional operating and capital expenditures required to bring the Mountain Pass facility to full operability. Shenghe also agreed to provide additional funding in the amount of $30.0 million to the Company pursuant to a separate letter agreement dated June 20, 2017 (the “Letter Agreement”) (the “First Additional Advance”), in connection with our acquisition of the Mountain Pass facility. In addition to the repayment of the First Additional Advance in cash, pursuant to the Letter Agreement, the Initial Prepayment Amount increased by $30.0 million. We refer to the aggregate prepayments made by Shenghe pursuant to the Original Offtake Agreement and the Framework Agreement (as defined below), as adjusted for Gross Profit Recoupment (as defined below) amounts and any other qualifying repayments to Shenghe, inclusive of the $30.0 million increase to the Initial Prepayment Amount, as the “Prepaid Balance.” As discussed below, the entrance into the Letter Agreement constituted a modification to the Original Offtake Agreement for accounting purposes (referred to as the “June 2017 Modification”), which ultimately resulted in the Shenghe Implied Discount (as defined below). Under the terms of these agreements, the amounts funded by Shenghe constitute prepayments for the rare earth products to be sold to Shenghe historically under the Original Offtake Agreement (and currently under the A&R Offtake Agreement, as defined below). Under the Original Offtake Agreement, upon the mine achieving certain milestones and being deemed commercially operational (which was achieved on July 1, 2019), we sold to Shenghe, and Shenghe purchased on a firm “take or pay” basis, all of the rare earth products produced at the Mountain Pass facility. Shenghe marketed and sold these products to customers, and retained the gross profits earned on subsequent sales. The gross profits were credited against the Prepaid Balance, and provided the means by which we repaid, and Shenghe recovered, such amounts (the “Gross Profit Recoupment”). Under the Original Offtake Agreement, we were obliged to sell all Mountain Pass facility rare earth products to Shenghe until Shenghe had fully recouped all of its prepayments (i.e., the Prepaid Balance is reduced to zero), at which point the Original Offtake Agreement would terminate automatically. As originally entered, the DMA was to become effective upon termination of the Original Offtake Agreement. The DMA provided for a distribution and marketing arrangement between the Company and Shenghe, subject to certain exceptions. We retained the right to distribute our products directly to certain categories of customers. As compensation for Shenghe’s distribution and marketing services, the DMA entitled Shenghe to a portion of the net profits from the sale of rare earth products produced at the Mountain Pass facility. Framework Agreement and Restructured Commercial Arrangements In May 2020, the Company entered into a framework agreement and amendment (the “Framework Agreement”) with Shenghe and Leshan Shenghe that significantly restructured the commercial arrangements and provided for, among other things, a revised funding amount and schedule to settle Shenghe’s prepayment obligations to the Company, as well as either the amendment or termination of the various agreements between the parties, as discussed below. Pursuant to the Framework Agreement, we entered into an amended and restated offtake agreement with Shenghe on May 19, 2020 (the “A&R Offtake Agreement”), which, upon effectiveness, superseded and replaced the Original Offtake Agreement, and we issued to Shenghe a warrant on June 2, 2020 (the “Shenghe Warrant”). Pursuant to the Framework Agreement, Shenghe funded the remaining portion of the Initial Prepayment Amount and agreed to fund an additional $35.5 million advance to us (the “Second Additional Advance” and together with the Initial Prepayment Amount, inclusive of the $30.0 million increase pursuant to the Letter Agreement, the “Offtake Advances”), which amounts were fully funded on June 5, 2020. The Shenghe Warrant was ultimately exchanged for shares of our Common Stock in connection with the Business Combination. Upon the funding of the remaining obligations on June 5, 2020, among other things, (i) the TSA and the DMA were terminated (as described below) and (ii) the A&R Offtake Agreement and the Shenghe Warrant became effective (such events are collectively referred to as the “June 2020 Modification”). Thus, at the present time, Leshan Shenghe’s and Shenghe’s involvement with the Company and the Mountain Pass facility consists of only the A&R Offtake Agreement. The A&R Offtake Agreement maintains the key take-or-pay, amounts owed on actual and deemed advances from Shenghe, and other terms of the Original Offtake Agreement, with the following material changes: (i) modifies the definition of “offtake products” in order to remove from the scope of that definition lanthanum, cerium and other rare earth products that do not meet the specifications agreed to under the A&R Offtake Agreement; (ii) as to the offtake products subject to the A&R Offtake Agreement, provides that if we sell such offtake products to a third party, then, until the Prepaid Balance has been reduced to zero, we will pay an agreed percentage of our revenue from such sale to Shenghe, to be credited against the amounts owed on Offtake Advances; (iii) replaces the Shenghe Sales Discount (as defined in Note 4, “Revenue Recognition” ) under the Original Offtake Agreement with a fixed monthly sales charge; (iv) provides that the purchase price to be paid by Shenghe for our rare earth products (a portion of which reduces the Prepaid Balance rather than being paid in cash) will be based on market prices (net of taxes, tariffs and certain other agreed charges) less applicable discounts, instead of our cash cost of production; (v) obliges us to pay Shenghe, on an annual basis, an amount equal to our annual net income, less any amounts recouped through the Gross Profit Recoupment mechanism over the course of the year, until the Prepaid Balance has been reduced to zero; (vi) obliges us to pay Shenghe the net after-tax profits from certain sales of assets until the Prepaid Balance has been reduced to zero (this obligation was previously contained in the TSA); and (vii) provides for certain changes to the payment, invoicing and delivery terms and procedures for products. The purchase price and other terms applicable to a quantity of offtake products are set forth in monthly purchase agreements between the Company and Shenghe. As with the Original Offtake Agreement, the A&R Offtake Agreement will terminate when Shenghe has fully recouped all of its prepayment funding. Following that termination, the Company will have no contractual arrangements with Shenghe for the distribution, marketing or sale of rare earth products. Accounting for the June 2017 Modification As discussed above, pursuant to the Letter Agreement, Shenghe agreed to provide additional funding via a short-term, non-interest-bearing note in the amount of $30.0 million to the Company (defined above as the “First Additional Advance”), which required repayment within one year. Furthermore, under the terms of the Letter Agreement, Shenghe became entitled to an additional $30.0 million recovery through an increase to the Prepaid Balance. Therefore, under the terms of the Letter Agreement, Shenghe would ultimately receive repayment of the short-term debt instrument from the Company, and also be entitled to realize an additional $30.0 million as a part of the contractual Gross Profit Recoupment from ultimate sales to its customers. The Company concluded that the $30.0 million proceeds received from Shenghe should be allocated between (i) the non-interest-bearing debt instrument and (ii) the existing revenue arrangement (under the terms of the Original Offtake Agreement) on a relative fair value basis. As a result of such analysis, the Company determined that the debt instrument had a relative fair value of $26.5 million and the modification to the revenue arrangement had a relative fair value of $3.5 million. The First Additional Advance was repaid in full by the Company in 2018. Based on the relationship between (i) the deemed proceeds the Company would ultimately receive from the Initial Prepayment Amount (adjusted for (a) the fair value of the preferred interest provided to Shenghe at the time of entering into the aforementioned commercial arrangements of $2.3 million and (b) the fair value allocated to the modification of the revenue arrangement of $3.5 million) and (ii) the contractual amount owed to Shenghe (i.e., the Prepaid Balance, which included the Initial Prepayment Amount and the additional $30.0 million adjustment to the Prepaid Balance in connection with the Letter Agreement) at the time, the June 2017 Modification resulted in an implied discount on the Company’s sales prices to Shenghe under the Original Offtake Agreement, for accounting purposes (the “Shenghe Implied Discount”). The Shenghe Implied Discount is applicable to Shenghe’s gross profit on the sales of rare earth products to its own customers (for sales made between July 2019 and early June 2020). That gross profit is a contractually determined amount based on Shenghe’s realized sales price (net of taxes, tariffs, and certain other adjustments, such as demurrage) compared to the agreed-upon cash cost Shenghe would pay to the Company. The Shenghe Implied Discount amounted to 36% of that contractually determined gross profit amount. See also Note 4, “Revenue Recognition.” Accounting for the June 2020 Modification As noted above, in June 2020, the Company renegotiated various aspects of its relationship with Shenghe and entered into the Framework Agreement to significantly restructure the aforementioned set of arrangements. Prior to the June 2020 Modification, for accounting purposes, the Original Offtake Agreement constituted a deferred revenue arrangement; however, as a result of the June 2020 Modification, the A&R Offtake Agreement constituted a debt obligation as well as provided for the issuance of the Shenghe Warrant. For further discussion of the deferred revenue arrangement, see Note 4, “Revenue Recognition,” and for further discussion of the debt obligation, see Note 8, “Debt Obligations.” Product Sales and Cost of Sales: The Company and Shenghe enter into separate product sales agreements in which Shenghe purchases all newly-produced material at specified prices. Product sales from these agreements were $59.7 million and $20.6 million for the three months ended March 31, 2021 and 2020, respectively, and are discussed in more detail in Note 4, “Revenue Recognition,” including amounts recognized as deferred revenue. Cost of sales, which includes shipping and freight, related to these agreements with Shenghe was $17.8 million and $12.5 million for the three months ended March 31, 2021 and 2020, respectively. Purchases: The Company purchases reagent products (produced by an unrelated third party manufacturer) used in the flotation process from Shenghe. Total purchases for the three months ended March 31, 2021 and 2020, totaled $0.7 million and $0.3 million, respectively. Royalty Agreement: In April 2017, MPMO entered into a 30-year mineral lease and license agreement with SNR (the “Royalty Agreement”) under which MPMO paid royalties to SNR in the amount of 2.5% of the gross proceeds from the sale of rare earth products made from ores extracted from the Mountain Pass mine, subject to a minimum non-refundable royalty of $0.5 million per year. At the time of entering into the Royalty Agreement, MPMO and SNR had shareholders common to both entities; however, they were not partners in business nor did they hold any other joint interest. In connection with the Business Combination, MPMO and SNR are both wholly-owned subsidiaries of the Company. Consequently, the intercompany transactions between MPMO and SNR after the date of the SNR Mineral Rights Acquisition and the Business Combination eliminate in consolidation, including the effects of the Royalty Agreement. Excluding payments of these minimums (which were treated as a reduction to the obligation), royalty expense was $0.5 million and the Company paid out $0.5 million for the three months ended March 31, 2020. Services Reimbursed: The Company reimbursed JHL Capital Group Holdings for travel-related expenses in the amount of less than $0.1 million during the three months ended March 31, 2021, and $0.1 million during the three months ended March 31, 2020. Accounts Receivable: As of March 31, 2021, and December 31, 2020, $13.8 million and $3.5 million of the accounts receivable, as stated on the unaudited Condensed Consolidated Balance Sheets, were receivable from a related party due to the Company’s sales agreements with Shenghe. Indebtedness: The Company’s related-party debt is described in Note 8, “Debt Obligations.”

REVENUE RECOGNITION

REVENUE RECOGNITION	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
REVENUE RECOGNITION	REVENUE RECOGNITION Sales to Shenghe Under the Original Offtake Agreement: Beginning in July 2019 and through early June 2020, the Company and Shenghe periodically agreed on a cash sales price for each metric ton of rare earth concentrate delivered by the Company, which was recognized as revenue upon each sale. This sales price was intended to approximate the Company’s cash cost of production. Sales during this period were made under the Original Offtake Agreement and were impacted by the Shenghe Implied Discount, which is discussed in Note 3, “Relationship and Agreements with Shenghe.” The Shenghe Implied Discount amounted to 36% of the difference between Shenghe’s realized price on its sales of rare earth products to its own customers (net of taxes, tariffs, and certain other adjustments, such as demurrage) and the agreed-upon cash cost for those products (i.e., its gross profit). In addition to the revenue we recognized from the cash sales prices, we also realized an amount of deferred revenue applicable to these sales equal to 64% of Shenghe’s gross profit. The full gross profit amount realized by Shenghe on such sales reduced the Prepaid Balance (and consequently, our contractual obligations to Shenghe). In addition, sales to Shenghe under the Original Offtake Agreement between July 2019 and early June 2020 typically provided Shenghe with a discount generally in the amount of between 3% and 6% of the initial cash price of our rare earth products sold in consideration of Shenghe’s sales efforts to resell our rare earth products (the “Shenghe Sales Discount”). The Shenghe Sales Discount was considered a reduction in the transaction price and thus was not recognized as revenue. Additionally, the Shenghe Sales Discount was not applied to reduce the Prepaid Balance; however, it was considered as part of Shenghe’s cost of acquiring our product in the calculation of Shenghe’s gross profit. Sales to Shenghe Under the A&R Offtake Agreement: Beginning after the June 2020 Modification, the cash purchase price (and other terms applicable to the quantity of products sold) are set forth in monthly purchase agreements with Shenghe. Furthermore, the June 2020 Modification provided that the cash purchase price to be paid by Shenghe for our rare earth products will be based on market prices (net of taxes, tariffs and certain other agreed charges) less applicable discounts, instead of our cash cost of production, as was the case with sales made under the Original Offtake Agreement. A portion of the sales price to Shenghe is in the form of debt repayment, with the remainder paid in cash. See Note 8, “Debt Obligations,” for further information. As a result of the June 2020 Modification, revenue recognized under the A&R Offtake Agreement after the June 2020 Modification does not include the Shenghe Implied Discount. In addition, rather than adjusting the sales price for the Shenghe Sales Discount, as was the case with sales made under the Original Offtake Agreement, revenue under the A&R Offtake Agreement is reduced by a fixed monthly sales charge (accounted for as a discount). Deferred Revenue: As mentioned in Note 3, “Relationship and Agreements with Shenghe,” the Original Offtake Agreement was accounted for as a deferred revenue arrangement, and the June 2020 Modification effectively replaced this deferred revenue arrangement with a debt obligation (see Note 8, “Debt Obligations” ). Significant activity for the deferred revenue balance (including current portion) was as follows: For the three months ended March 31, (in thousands) 2021 2020 Opening balance (1) $ — $ 35,543 Prepayments received (2) — 1,500 Prepayments on sales (3) — 5,212 Revenue recognized (4) — (2,191) Ending balance $ — $ 40,064 (1) Of the amount for the three months ended March 31, 2020, $6.6 million was classified as current based on when such amount was expected to be realized. (2) Amount for the three months ended March 31, 2020, relates to the contractual commitment for Shenghe to provide funds to the Company (the Initial Prepayment Amount). (3) Amount for the three months ended March 31, 2020, relates to a prepayment made by Shenghe to the Company in advance of recognizing the revenue associated with the sale of products. (4) As discussed above, for sales made to Shenghe during the period from July 2019 through early June 2020, as a result of the Shenghe Implied Discount, we recognized an amount of deferred revenue applicable to such sales equal to 64% of the gross profit realized by Shenghe on sales of this product to its own customers. Tariff-Related Rebates: In May 2020, the government of the People’s Republic of China suspended certain tariffs that had been charged to consignees of our product on product imports retroactive to March 2020, which affected the sales price the Company realized. In addition, Shenghe began negotiating for certain tariff rebates from sales prior to March 2020, which affected Shenghe’s realized prices, and thus the contractual Prepaid Balance. These, in turn, affected the Company’s realized prices on prior sales. While additional tariff rebates were possible, the Company did not have insight into Shenghe’s negotiations or their probability of success, and such negotiations were outside of the Company’s control. Thus, the Company fully constrained estimates of any future tariff rebates that may have been realized at that time. In January 2021, the Company received additional information from Shenghe regarding its successful negotiation of additional tariff rebates. Consequently, the Company revised its estimates of variable consideration and recognized $2.0 million of revenue. Since this rebate was recognized after the June 2020 Modification, this amount was treated as a reduction to the principal balance of the debt obligation, partially offset by a proportionate reduction in the related debt discount, as discussed in Note 8 , “Debt Obligations.”

RESTRICTED CASH

RESTRICTED CASH	3 Months Ended
	Mar. 31, 2021
Cash and Cash Equivalents [Abstract]
RESTRICTED CASH	RESTRICTED CASH The Company’s restricted cash balances were as follows: March 31, 2021 December 31, 2020 (in thousands) Restricted cash, current $ 3,765 $ 3,688 Restricted cash, non-current 9,115 9,100 Total restricted cash $ 12,880 $ 12,788 The current restricted cash, which is included in “Prepaid expenses and other current assets” within the unaudited Condensed Consolidated Balance Sheets, principally relates to cash held in escrow. The non-current restricted cash is cash collateral posted for closure and post-closure surety bonding for the Mountain Pass site and a trust established with the California Department of Resources Recycling and Recovery, which is the state of California’s recycling and waste management program, for a closed onsite landfill.

INVENTORIES

INVENTORIES	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
INVENTORIES	INVENTORIES The Company’s inventories consisted of the following: March 31, 2021 December 31, 2020 (in thousands) Materials and supplies (1) $ 6,362 $ 5,124 In-process (2) 26,356 24,524 Finished goods (3) 2,380 2,624 Total inventory $ 35,098 $ 32,272 (1) Comprised of raw materials, spare parts, reagent chemicals, and packaging materials used in the production of rare earth products (2) Primarily comprised of mined ore stockpiles and bastnaesite ore in various stages of the production process that are drawn down based on the demands of our mine production plan (3) Primarily comprised of packaged bastnaesite ore that is ready for sale

PROPERTY, PLANT AND EQUIPMENT

PROPERTY, PLANT AND EQUIPMENT	3 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT	PROPERTY, PLANT AND EQUIPMENT The Company’s property, plant and equipment primarily relates to the Mountain Pass facility and open-pit mine. In addition to the mine, the facility includes a crusher and mill/flotation plant, mineral recovery and separation plants, tailings processing and storage facilities, on-site evaporation ponds, a combined heat and power plant, water treatment facilities, a Chlor-Alkali plant, as well as laboratory facilities to support research and development activities, offices, warehouses and support infrastructures. Property, plant and equipment consisted of the following: March 31, 2021 December 31, 2020 (in thousands) Machinery and equipment $ 33,677 $ 22,911 Buildings 3,147 2,953 Land and land improvements 8,938 6,534 Assets under construction 70,125 46,814 Mineral rights 437,654 437,654 Property, plant and equipment 553,541 516,866 Less: Accumulated depreciation and depletion (21,037) (14,892) Property, plant and equipment, net $ 532,504 $ 501,974 The Company capitalized expenditures of $27.3 million and $1.0 million for the three months ended March 31, 2021 and 2020, respectively. Most of these expenditures related to vehicles, machinery, equipment, and certain other capital projects at the mine. Interest capitalized was less than $0.1 million for the three months ended March 31, 2021. No interest was capitalized for the three months ended March 31, 2020. In February 2021, the Company acquired equipment, including trucks and loaders, in the aggregate amount of $9.4 million, which was purchased through seller-financed equipment notes. See also Note 8, “Debt Obligations,” and Note 18, “Supplemental Cash Flow Information.” Depreciation expense for the three months ended March 31, 2021 and 2020, was $1.5 million and $1.2 million, respectively. Depletion expense for the three months ended March 31, 2021 and 2020, was $4.5 million and less than $0.1 million, respectively. There were no impairments recognized for the three months ended March 31, 2021 and 2020.

DEBT OBLIGATIONS

DEBT OBLIGATIONS	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
DEBT OBLIGATIONS	DEBT OBLIGATIONS The Company’s current and non-current portions of long-term debt were as follows: March 31, 2021 December 31, 2020 (in thousands) Long-term debt Convertible Notes due 2026 $ 690,000 $ — Paycheck Protection Loan 3,364 3,364 Less: Unamortized debt issuance costs (17,677) — Net carrying amount 675,687 3,364 Less: Current installments of long-term debt (3,105) (2,403) Long-term debt, net of current portion $ 672,582 $ 961 Long-term debt to related party Offtake Advances $ 60,401 $ 71,843 Less: Unamortized debt discount (4,211) (5,393) Net carrying amount 56,190 66,450 Less: Current installments of long-term debt to related party (38,457) (22,070) Long-term debt to related party, net of current portion $ 17,733 $ 44,380 Convertible Notes On March 26, 2021, the Company issued $690.0 million aggregate principal amount of 0.25% unsecured green convertible senior notes that mature, unless earlier converted, redeemed or repurchased, on April 1, 2026 (the “Convertible Notes”), at a price of par. Interest on the Convertible Notes is payable on April 1 st and October 1 st of each year, beginning on October 1, 2021. The gross proceeds received by the Company for the sale of the Convertible Notes were offset by $17.4 million of debt issuance costs paid as of March 31, 2021. The Convertible Notes are convertible into shares of the Company’s Common Stock at an initial conversion price of $44.28 per share, or 22.5861 shares, per $1,000 principal amount of notes, subject to adjustment upon the occurrence of certain corporate events. However, in no event will the conversion exceed 28.5714 shares of Common Stock per $1,000 principal amount of notes. As of March 31, 2021, based on the initial conversion price, the maximum number of shares that could be issued to satisfy the conversion feature of the Convertible Notes was 19,714,266 and the amount by which the Convertible Notes’ if-converted value exceeded its principal amount was $18.7 million. Prior to January 1, 2026, at their election, holders of the Convertible Notes may convert their outstanding notes under the following circumstances: i) during any calendar quarter commencing with the third quarter of 2021 if the last reported sale price of the Company’s Common Stock for at least 20 trading days (whether or not consecutive) during the period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; ii) during the five business day period after any five consecutive trading day period (the “measurement period”) in which the trading price (as defined below) per $1,000 principal amount of Convertible Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s Common Stock and the conversion rate on each such trading day; iii) if we call any or all of the Convertible Notes for redemption, at any time prior to the close of business on the scheduled trading day immediately preceding the redemption date; or iv) upon the occurrence of specified corporate events set forth in the indenture governing the Convertible Notes. On or after January 1, 2026, and prior to the maturity date of the Convertible Notes, holders may convert their outstanding notes at any time, regardless of the foregoing circumstances. The Convertible Notes may, at the Company’s election, be settled in cash, shares of Common Stock of the Company, or a combination thereof. The Company has the option to redeem the Convertible Notes, in whole or in part, beginning on April 5, 2024. If we undergo a fundamental change (as defined in the indenture governing the Convertible Notes), holders may require us to repurchase for cash all or any portion of their outstanding notes at a price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In addition, following certain corporate events that occur prior to the maturity date of the Convertible Notes or if we deliver a notice of redemption, we will, in certain circumstances, increase the conversion rate for holders who elect to convert their outstanding notes in connection with such corporate event or notice of redemption, as the case may be. As of March 31, 2021, the principal amount of the Convertible Notes was $690.0 million and the associated unamortized debt issuance costs was $17.7 million, resulting in a net carrying amount of $672.3 million. Paycheck Protection Loan In April 2020, the Company obtained a loan of $3.4 million pursuant to the Paycheck Protection Program (the “PPP”) under Division A, Title I of the CARES Act, which was enacted in March 2020 (the “Paycheck Protection Loan” or the “Loan”). The Paycheck Protection Loan, which was in the form of a note dated April 15, 2020, issued by CIBC Bank USA, matures on April 14, 2022, and bears interest at a rate of 1% per annum. Under the terms of the PPP, the Loan may be forgiven if the funds are used for qualifying expenses as described in the CARES Act, which include payroll costs, costs used to continue group health care benefits, rent and utilities. In November 2020, we applied for forgiveness of the entire balance in accordance with the requirements and limitations under the CARES Act and Small Business Administration (“SBA”) regulations and requirements. Based on guidance from the U.S. Department of the Treasury, since the proceeds exceeded $2.0 million, our application is subject to audit by the SBA. We are currently awaiting a determination on forgiveness of the Paycheck Protection Loan. Payments on the Loan are deferred until the SBA determines the amount to be forgiven. Offtake Advances In connection with the June 2020 Modification, which is discussed in Note 3, “Relationship and Agreements with Shenghe,” Shenghe agreed to fund an additional $35.5 million advance to the Company (previously defined as the “Second Additional Advance”) and the Company issued the Shenghe Warrant. For accounting purposes, the June 2020 Modification effectively replaced the deferred revenue arrangement relating to the Original Offtake Agreement with a debt obligation relating to the A&R Offtake Agreement and the issuance of the Shenghe Warrant. Under the A&R Offtake Agreement, a portion of the sales prices of products sold to Shenghe is paid in the form of debt reduction, rather than cash. In addition, the Company must pay the following amounts to Shenghe in cash to reduce the debt obligation until repaid in full: (i) an agreed-upon percentage of sales of products to parties other than Shenghe under the A&R Offtake Agreement; (ii) 100% of net profits from asset sales; and (iii) 100% of net income determined under GAAP, less the tax-effected amount of total non-cash recoupment from sales of products to Shenghe. For the three months ended March 31, 2021, $9.2 million of the sales prices of products sold to Shenghe was paid in the form of debt reduction (see Note 18, “Supplemental Cash Flow Information” ). No amounts were required to be paid based on sales to other parties or asset sales. After consideration of the Second Additional Advance, the outstanding balance on the Offtake Advances, as of the date of the June 2020 Modification, was $94.0 million. Since the debt obligation was recorded at fair value, the result was a debt discount of $8.3 million. The A&R Offtake Agreement does not have a stated rate (and is non-interest-bearing), and repayment is contingent on a number of factors, including market prices realized by Shenghe, the Company’s sales to other parties, asset sales, and the Company’s annual net income. The imputed interest rate is a function of this discount taken together with our expectations about the timing of the anticipated reductions of the principal balance. Based on current forecasts, the Company expects to repay the obligation within the next two years. As of March 31, 2021, and December 31, 2020, $42.5 million and $25.7 million of the principal amount, respectively, was classified as current based on the Company’s expectations of the timing of repayment. The actual amounts repaid may differ in timing and amount from the Company’s estimates and is updated each reporting period to determine the imputed interest rate, which will likely differ from the current estimated rate. The Company has determined that it will recognize adjustments from these estimates following a prospective method. Under the prospective method, the Company will update its estimate of the effective interest rate in future periods based on revised estimates of the timing of remaining principal reductions at that time. The updated rate will be the discount rate that equates the present value of those revised estimates of remaining reductions with the carrying amount of the debt, and it will be used to recognize interest expense for the remaining periods. Under the prospective method, the effective interest rate is not constant, and changes are recognized prospectively as an adjustment to the effective yield. The effective rate applicable from the June 5, 2020, inception to March 31, 2021, was between 4.41% and 6.59%. Based on the revised estimates of the timing of the remaining principal reductions as of March 31, 2021, the Company updated its estimate of the effective interest rate to 10.37% to be applied prospectively to future periods. As discussed in Note 4, “Revenue Recognition,” in January 2021, the Company was informed of a $2.2 million tariff rebate Shenghe received, which increased the gross profit earned by Shenghe on certain prior period sales. As a result, for the three months ended March 31, 2021, the Company recorded a reduction in the principal amount of the debt obligation of $2.2 million and the corresponding debt discount of $0.2 million. Equipment Notes The Company has entered into several financing agreements for the purchase of equipment, including trucks, tractors, loaders, graders, and various other machinery, including agreements entered into in February 2021 (as further discussed below). The Company’s equipment notes, which are secured by the purchased equipment, have terms of between 4 to 5 years and interest rates of between 0.0% and 6.5% per annum. In February 2021, we entered into financing agreements for the purchase of equipment, including trucks and loaders, in the aggregate amount of $9.7 million, including an amount for the associated extended warranties. These equipment notes have terms of 5 years and interest rates of 4.5% per annum with monthly payments commencing in April 2021. The current and non-current portions of the equipment notes, which are included within the unaudited Condensed Consolidated Balance Sheets in “Other current liabilities” and “Other non-current liabilities,” respectively, were as follows: March 31, 2021 December 31, 2020 (in thousands) Equipment notes Current $ 2,614 $ 835 Non-current 8,997 1,267 $ 11,611 $ 2,102 Interest expense, net Interest expense, net, was as follows: For the three months ended March 31, (in thousands) 2021 2020 Interest expense $ 1,165 $ 803 Capitalized interest (11) — Interest expense, net $ 1,154 $ 803 Interest expense related to the Convertible Notes was as follows: For the three months ended March 31, (in thousands) 2021 2020 Coupon interest $ 24 $ — Amortization of debt issuance costs 48 — Convertible Notes interest expense $ 72 $ — The debt issuance costs are being amortized to interest expense over the term of the Convertible Notes at an effective interest rate of 0.51%. The remaining term of the Convertible Notes was 5.0 years as of March 31, 2021. As of March 31, 2021, none of the agreements or indentures governing our indebtedness contain financial covenants.

LEASE OBLIGATIONS

LEASE OBLIGATIONS	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
LEASE OBLIGATIONS	LEASE OBLIGATIONS The Company has operating and finance leases for certain office space, vehicles and equipment used in its operations, none of which are with related parties. Supplemental disclosure for the unaudited Condensed Consolidated Balance Sheets related to the Company’s operating and finance leases is as follows: Location on Unaudited Condensed Consolidated Balance Sheets March 31, 2021 December 31, 2020 (in thousands) Operating Leases: Right-of-use assets Other non-current assets $ 579 $ 1,090 Operating lease liability, current Other current liabilities $ 333 $ 761 Operating lease liability, non-current Other non-current liabilities 271 357 Total operating lease liabilities $ 604 $ 1,118 Finance Leases: Right-of-use assets Finance lease right-of-use assets $ 974 $ 1,028 Finance lease liability, current Current portion of finance lease liabilities $ 279 $ 266 Finance lease liability, non-current Finance lease liabilities, net of current portion 687 736 Total finance lease liabilities $ 966 $ 1,002
LEASE OBLIGATIONS	LEASE OBLIGATIONS The Company has operating and finance leases for certain office space, vehicles and equipment used in its operations, none of which are with related parties. Supplemental disclosure for the unaudited Condensed Consolidated Balance Sheets related to the Company’s operating and finance leases is as follows: Location on Unaudited Condensed Consolidated Balance Sheets March 31, 2021 December 31, 2020 (in thousands) Operating Leases: Right-of-use assets Other non-current assets $ 579 $ 1,090 Operating lease liability, current Other current liabilities $ 333 $ 761 Operating lease liability, non-current Other non-current liabilities 271 357 Total operating lease liabilities $ 604 $ 1,118 Finance Leases: Right-of-use assets Finance lease right-of-use assets $ 974 $ 1,028 Finance lease liability, current Current portion of finance lease liabilities $ 279 $ 266 Finance lease liability, non-current Finance lease liabilities, net of current portion 687 736 Total finance lease liabilities $ 966 $ 1,002

ASSET RETIREMENT AND ENVIRONMEN

ASSET RETIREMENT AND ENVIRONMENTAL OBLIGATIONS	3 Months Ended
	Mar. 31, 2021
Asset Retirement Obligation And Environmental Remediation Obligations [Abstract]
ASSET RETIREMENT AND ENVIRONMENTAL OBLIGATIONS	ASSET RETIREMENT AND ENVIRONMENTAL OBLIGATIONS Asset Retirement Obligations Management estimated asset retirement obligations based on the requirements to reclaim its mine asset and related Mountain Pass facility. Minor reclamation activities related to discrete portions of our operations are ongoing. As of March 31, 2021, management estimates a significant portion of the cash outflows for the major reclamation and the retirement of the Mountain Pass facility will be incurred beginning in 2043. As of March 31, 2021, the credit-adjusted risk-free rate ranged between 7.1% and 8.2% depending on the timing of expected settlement and when the layer or increment was recognized. There were no increments or decrements for the three months ended March 31, 2021 and 2020. The balance as of March 31, 2021, and December 31, 2020, included current portions of $0.1 million. The total estimated future undiscounted cash flows required to satisfy the asset retirement obligations were $141.6 million and $142.3 million as of March 31, 2021, and December 31, 2020, respectively. The Company is required to provide the applicable government agencies with financial assurances relating to the closure and reclamation obligations. As of March 31, 2021, and December 31, 2020, the Company had financial assurance requirements of $38.5 million and $38.4 million, respectively, which were satisfied with surety bonds placed with the California state and regional agencies that are partially secured by restricted cash. Environmental Obligations The Company assumed certain environmental remediation liabilities related to the monitoring of groundwater contamination. The Company engaged an environmental consultant to develop a remediation plan and remediation cost projections based upon that plan. Utilizing the remediation plan developed by the environmental consultant, management developed an estimate of future cash payments for the remediation plan. As of March 31, 2021, management estimated the cash outflows related to these environmental activities will be incurred annually over the next 27 years. The Company’s environmental remediation liabilities are measured at the expected value of future cash outflows discounted to their present value using a discount rate of 2.93%. There were no increments or decrements for the three months ended March 31, 2021 and 2020.

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXESThe Company calculates the provision for income taxes during interim reporting periods by applying an estimate of the annual effective tax rate to its year-to-date pretax book income or loss. The tax effects of discrete items, including but not limited to, excess tax benefits associated with stock-based compensation, valuation allowance adjustments based on new evidence and enactment of tax laws, are reported in the interim period in which they occur. The effective tax rate (income taxes as a percentage of income or loss before income taxes) including discrete items was 21.8% for the three months ended March 31, 2021, as compared to 0.0% for the three months ended March 31, 2020, due to a full valuation allowance as of March 31, 2020. Our effective income tax rate can vary from period to period depending on, among other factors, percentage depletion, executive compensation deduction limitations, other permanent book/tax items, and changes to our valuation allowance, if any. Certain of these and other factors, including our history and projections of pretax earnings, are considered in assessing our ability to realize our net deferred tax assets.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES In the ordinary course of business, the Company becomes party to lawsuits, administrative proceedings, and government investigations, including environmental, regulatory, and other matters. The Company’s management does not believe that any such matters, individually or in the aggregate, will have a material adverse effect on the Company’s business, financial condition, results of operations, or cash flows. In January 2019, a former employee filed a complaint with the California Labor & Workforce Development Agency alleging numerous violations of California labor law, and subsequently filed a representative action against the Company. The Company disputes the plaintiff’s allegations and has retained counsel to represent it in the litigation. The Company is unable to estimate a range of loss, if any, at this time. If an unfavorable outcome were to occur in the case, it is possible that the impact could be material in respect of the Company’s results of operations in the period in which any such outcome becomes probable and reasonably estimable.

STOCKHOLDERS_ EQUITY

STOCKHOLDERS’ EQUITY	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
STOCKHOLDERS’ EQUITY	STOCKHOLDERS’ EQUITY Common Stock and Preferred Stock On November 17, 2020, in connection with the consummation of the Business Combination, FVAC amended and restated its first amended and restated certificate of incorporation (the “Second Amended and Restated Certificate of Incorporation”). Pursuant to the terms of the Second Amended and Restated Certificate of Incorporation, the Company increased the number of authorized shares of all classes of capital stock from 221,000,000 shares to 500,000,000, consisting of (i) 450,000,000 shares of common stock (previously defined as “Common Stock”) and (ii) 50,000,000 shares of preferred stock, each with a par value of $0.0001 per share. Public Warrants Warrants to purchase 11,499,968 shares of the Company’s Common Stock at $11.50 per share were issued during FVAC’s initial public offering (“IPO”) (the “Public Warrants”). The Public Warrants became exercisable on May 4, 2021, which was 12 months from the closing of FVAC’s IPO. The Public Warrants expire five years after the completion of the Business Combination or earlier upon redemption or liquidation. These warrants qualify as equity instruments as they are indexed to the Company’s stock and settlement in shares is within the Company’s control. Accordingly, the Public Warrants are included in “Additional paid-in capital” within the Company’s unaudited Condensed Consolidated Balance Sheets as of March 31, 2021, and December 31, 2020. Beginning on May 4, 2021, if the reported last sale price of the Company’s Common Stock equals or exceeds $18.00 per share for any 20 trading days within a 30-trading day period ending three Upon calling the Public Warrants for redemption, management has the option to require all holders that wish to exercise the Public Warrants to do so on a cashless basis. The exercise price and number of shares of common stock issuable upon exercise of the warrants may be adjusted in certain circumstances including in the event of a stock dividend, or recapitalization, reorganization, merger or consolidation. The warrants will not be adjusted for issuance of common stock at a price below its exercise price. The Company is not required to net cash settle the Public Warrants. On May 4, 2021, the Company announced that it will redeem all outstanding Public Warrants. For further discussion, see Note 19, “ Subsequent Events. ”

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION 2020 Incentive Plan: In November 2020, the Company’s stockholders approved the MP Materials Corp. 2020 Stock Incentive Plan (the “2020 Incentive Plan”), which permits the Company to issue stock options (incentive and/or non-qualified); stock appreciation rights; restricted stock, restricted stock units, and other stock awards; and performance awards. As of March 31, 2021, there were 7,160,148 shares available for future grants under the 2020 Incentive Plan. Stock-Based Compensation Expense: During the three months ended March 31, 2021, the Company recognized $5.7 million of stock-based compensation expense, which is principally included in the unaudited Condensed Consolidated Statements of Operations within “General and administrative.” There was no stock-based compensation expense recognized for the three months ended March 31, 2020.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS ASC Topic 820, “Fair Value Measurements and Disclosures” (“ASC 820”), establishes a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). The three levels of the fair value hierarchy are described below: Level 1 Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; Level 2 Quoted prices in markets that are not active, quoted prices for similar assets or liabilities in active markets, quoted prices or inputs that are observable, either directly or indirectly, for substantially the full term of the asset or liability and model-based valuation techniques (e.g., the Black-Scholes model) for which all significant inputs are observable in active markets. Level 3 Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (supported by little or no market activity). The Company’s assessment of the significance of a particular input to the fair value measurement requires judgment and may affect the valuation of assets and liabilities and their placement within the fair value hierarchy. The following methods and assumptions are used to estimate the fair value of each class of financial instruments for which it is practicable to estimate. The fair value of the Company’s accounts receivable, accounts payable, short-term debt and accrued liabilities approximates the carrying amounts because of the immediate or short-term maturity of these financial instruments. Cash, Cash Equivalents and Restricted Cash The Company’s cash, cash equivalents and restricted cash are classified within Level 1 of the fair value hierarchy. The carrying amounts reported in the unaudited Condensed Consolidated Balance Sheets approximate the fair value of cash, cash equivalents and restricted cash due to the short-term nature of these assets. Convertible Notes The fair value of the Company’s Convertible Notes is estimated based on quoted prices in active markets and is classified as a Level 1 measurement. Offtake Advances The Company’s Offtake Advances balance is classified within Level 3 of the fair value hierarchy because there are unobservable inputs that follow an imputed interest rate model to calculate the amortization of the embedded debt discount, which is recognized as non-cash interest expense, by estimating the timing of anticipated payments and reductions of the debt principal balance. This model-based valuation technique, for which there are unobservable inputs, was used to estimate the fair value of the liability balance classified within Level 3 of the fair value hierarchy as of March 31, 2021, and December 31, 2020. Equipment Notes The Company’s equipment notes are classified within Level 2 of the fair value hierarchy because there are inputs that are directly observable for substantially the full term of the liability. Model-based valuation techniques for which all significant inputs are observable in active markets were used to calculate the fair values of liabilities classified within Level 2 of the fair value hierarchy as of March 31, 2021, and December 31, 2020. As required by ASC 820, assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The carrying amounts and estimated fair values by input level of the Company’s financial instruments were as follows: March 31, 2021 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 1,181,515 $ 1,181,515 $ 1,181,515 $ — $ — Restricted cash $ 12,880 $ 12,880 $ 12,880 $ — $ — Financial liabilities: Convertible Notes $ 672,323 $ 711,882 $ 711,882 $ — $ — Offtake Advances $ 56,190 $ 58,462 $ — $ — $ 58,462 Equipment notes $ 11,611 $ 11,210 $ — $ 11,210 $ — December 31, 2020 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 519,652 $ 519,652 $ 519,652 $ — $ — Restricted cash $ 12,788 $ 12,788 $ 12,788 $ — $ — Financial liabilities: Offtake Advances $ 66,450 $ 68,151 $ — $ — $ 68,151 Equipment notes $ 2,102 $ 2,077 $ — $ 2,077 $ —

EARNINGS PER SHARE

EARNINGS PER SHARE	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
EARNINGS PER SHARE	EARNINGS PER SHARE Basic EPS is computed by dividing net income by the weighted-average number of common shares outstanding during the period. Diluted EPS is computed by dividing net income by the weighted-average number of common shares outstanding plus the effect of dilutive potential common shares outstanding during the period using the treasury stock method or the if-converted method, as applicable. The following table reconciles the weighted-average common shares outstanding used in the calculation of basic EPS to the weighted-average common shares outstanding used in the calculation of diluted EPS: For the three months ended March 31, 2021 2020 Weighted-average shares outstanding, basic 168,922,566 66,556,975 Assumed conversion of Public Warrants 7,922,357 — Assumed conversion of Convertible Notes 1,038,961 — Assumed conversion of restricted stock 1,176,133 — Assumed conversion of restricted stock units 259,472 — Weighted-average shares outstanding, diluted 179,319,489 66,556,975 The following table presents the calculation of basic and diluted EPS for the Company’s Common Stock: For the three months ended March 31, (in thousands, except share and per share data) 2021 2020 Calculation of basic EPS: Net income $ 16,119 $ 1,925 Weighted-average shares outstanding, basic 168,922,566 66,556,975 Basic EPS $ 0.10 $ 0.03 Calculation of diluted EPS: Net income $ 16,119 $ 1,925 Interest expense, net of tax (1) : Convertible Notes 57 — Diluted income $ 16,176 $ 1,925 Weighted-average shares outstanding, diluted 179,319,489 66,556,975 Diluted EPS $ 0.09 $ 0.03 (1) The three months ended March 31, 2021, was tax-effected at a rate of 21.8%. As discussed in Note 8, “Debt Obligations,” the Convertible Notes were issued in March 2021; therefore, no adjustment is required for the three months ended March 31, 2020.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATIONSHIP AND AGREEMENTS WITH SHENGHE Original Commercial Agreements In May 2017, prior to our acquisition of the Mountain Pass facility, we entered into a set of commercial arrangements with Shenghe, which principally consisted of a technical services agreement (the “TSA”), an offtake agreement (the “Original Offtake Agreement”), and a distribution and marketing agreement (the “DMA”). The Original Offtake Agreement required Shenghe to advance us an initial $50.0 million (the “Initial Prepayment Amount”) to fund the restart of operations at the mine and the TSA required Shenghe to fund any additional operating and capital expenditures required to bring the Mountain Pass facility to full operability. Shenghe also agreed to provide additional funding in the amount of $30.0 million to the Company pursuant to a separate letter agreement dated June 20, 2017 (the “Letter Agreement”) (the “First Additional Advance”), in connection with our acquisition of the Mountain Pass facility. In addition to the repayment of the First Additional Advance in cash, pursuant to the Letter Agreement, the Initial Prepayment Amount increased by $30.0 million. We refer to the aggregate prepayments made by Shenghe pursuant to the Original Offtake Agreement and the Framework Agreement (as defined below), as adjusted for Gross Profit Recoupment (as defined below) amounts and any other qualifying repayments to Shenghe, inclusive of the $30.0 million increase to the Initial Prepayment Amount, as the “Prepaid Balance.” As discussed below, the entrance into the Letter Agreement constituted a modification to the Original Offtake Agreement for accounting purposes (referred to as the “June 2017 Modification”), which ultimately resulted in the Shenghe Implied Discount (as defined below). Under the terms of these agreements, the amounts funded by Shenghe constitute prepayments for the rare earth products to be sold to Shenghe historically under the Original Offtake Agreement (and currently under the A&R Offtake Agreement, as defined below). Under the Original Offtake Agreement, upon the mine achieving certain milestones and being deemed commercially operational (which was achieved on July 1, 2019), we sold to Shenghe, and Shenghe purchased on a firm “take or pay” basis, all of the rare earth products produced at the Mountain Pass facility. Shenghe marketed and sold these products to customers, and retained the gross profits earned on subsequent sales. The gross profits were credited against the Prepaid Balance, and provided the means by which we repaid, and Shenghe recovered, such amounts (the “Gross Profit Recoupment”). Under the Original Offtake Agreement, we were obliged to sell all Mountain Pass facility rare earth products to Shenghe until Shenghe had fully recouped all of its prepayments (i.e., the Prepaid Balance is reduced to zero), at which point the Original Offtake Agreement would terminate automatically. As originally entered, the DMA was to become effective upon termination of the Original Offtake Agreement. The DMA provided for a distribution and marketing arrangement between the Company and Shenghe, subject to certain exceptions. We retained the right to distribute our products directly to certain categories of customers. As compensation for Shenghe’s distribution and marketing services, the DMA entitled Shenghe to a portion of the net profits from the sale of rare earth products produced at the Mountain Pass facility. Framework Agreement and Restructured Commercial Arrangements In May 2020, the Company entered into a framework agreement and amendment (the “Framework Agreement”) with Shenghe and Leshan Shenghe that significantly restructured the commercial arrangements and provided for, among other things, a revised funding amount and schedule to settle Shenghe’s prepayment obligations to the Company, as well as either the amendment or termination of the various agreements between the parties, as discussed below. Pursuant to the Framework Agreement, we entered into an amended and restated offtake agreement with Shenghe on May 19, 2020 (the “A&R Offtake Agreement”), which, upon effectiveness, superseded and replaced the Original Offtake Agreement, and we issued to Shenghe a warrant on June 2, 2020 (the “Shenghe Warrant”). Pursuant to the Framework Agreement, Shenghe funded the remaining portion of the Initial Prepayment Amount and agreed to fund an additional $35.5 million advance to us (the “Second Additional Advance” and together with the Initial Prepayment Amount, inclusive of the $30.0 million increase pursuant to the Letter Agreement, the “Offtake Advances”), which amounts were fully funded on June 5, 2020. The Shenghe Warrant was ultimately exchanged for shares of our Common Stock in connection with the Business Combination. Upon the funding of the remaining obligations on June 5, 2020, among other things, (i) the TSA and the DMA were terminated (as described below) and (ii) the A&R Offtake Agreement and the Shenghe Warrant became effective (such events are collectively referred to as the “June 2020 Modification”). Thus, at the present time, Leshan Shenghe’s and Shenghe’s involvement with the Company and the Mountain Pass facility consists of only the A&R Offtake Agreement. The A&R Offtake Agreement maintains the key take-or-pay, amounts owed on actual and deemed advances from Shenghe, and other terms of the Original Offtake Agreement, with the following material changes: (i) modifies the definition of “offtake products” in order to remove from the scope of that definition lanthanum, cerium and other rare earth products that do not meet the specifications agreed to under the A&R Offtake Agreement; (ii) as to the offtake products subject to the A&R Offtake Agreement, provides that if we sell such offtake products to a third party, then, until the Prepaid Balance has been reduced to zero, we will pay an agreed percentage of our revenue from such sale to Shenghe, to be credited against the amounts owed on Offtake Advances; (iii) replaces the Shenghe Sales Discount (as defined in Note 4, “Revenue Recognition” ) under the Original Offtake Agreement with a fixed monthly sales charge; (iv) provides that the purchase price to be paid by Shenghe for our rare earth products (a portion of which reduces the Prepaid Balance rather than being paid in cash) will be based on market prices (net of taxes, tariffs and certain other agreed charges) less applicable discounts, instead of our cash cost of production; (v) obliges us to pay Shenghe, on an annual basis, an amount equal to our annual net income, less any amounts recouped through the Gross Profit Recoupment mechanism over the course of the year, until the Prepaid Balance has been reduced to zero; (vi) obliges us to pay Shenghe the net after-tax profits from certain sales of assets until the Prepaid Balance has been reduced to zero (this obligation was previously contained in the TSA); and (vii) provides for certain changes to the payment, invoicing and delivery terms and procedures for products. The purchase price and other terms applicable to a quantity of offtake products are set forth in monthly purchase agreements between the Company and Shenghe. As with the Original Offtake Agreement, the A&R Offtake Agreement will terminate when Shenghe has fully recouped all of its prepayment funding. Following that termination, the Company will have no contractual arrangements with Shenghe for the distribution, marketing or sale of rare earth products. Accounting for the June 2017 Modification As discussed above, pursuant to the Letter Agreement, Shenghe agreed to provide additional funding via a short-term, non-interest-bearing note in the amount of $30.0 million to the Company (defined above as the “First Additional Advance”), which required repayment within one year. Furthermore, under the terms of the Letter Agreement, Shenghe became entitled to an additional $30.0 million recovery through an increase to the Prepaid Balance. Therefore, under the terms of the Letter Agreement, Shenghe would ultimately receive repayment of the short-term debt instrument from the Company, and also be entitled to realize an additional $30.0 million as a part of the contractual Gross Profit Recoupment from ultimate sales to its customers. The Company concluded that the $30.0 million proceeds received from Shenghe should be allocated between (i) the non-interest-bearing debt instrument and (ii) the existing revenue arrangement (under the terms of the Original Offtake Agreement) on a relative fair value basis. As a result of such analysis, the Company determined that the debt instrument had a relative fair value of $26.5 million and the modification to the revenue arrangement had a relative fair value of $3.5 million. The First Additional Advance was repaid in full by the Company in 2018. Based on the relationship between (i) the deemed proceeds the Company would ultimately receive from the Initial Prepayment Amount (adjusted for (a) the fair value of the preferred interest provided to Shenghe at the time of entering into the aforementioned commercial arrangements of $2.3 million and (b) the fair value allocated to the modification of the revenue arrangement of $3.5 million) and (ii) the contractual amount owed to Shenghe (i.e., the Prepaid Balance, which included the Initial Prepayment Amount and the additional $30.0 million adjustment to the Prepaid Balance in connection with the Letter Agreement) at the time, the June 2017 Modification resulted in an implied discount on the Company’s sales prices to Shenghe under the Original Offtake Agreement, for accounting purposes (the “Shenghe Implied Discount”). The Shenghe Implied Discount is applicable to Shenghe’s gross profit on the sales of rare earth products to its own customers (for sales made between July 2019 and early June 2020). That gross profit is a contractually determined amount based on Shenghe’s realized sales price (net of taxes, tariffs, and certain other adjustments, such as demurrage) compared to the agreed-upon cash cost Shenghe would pay to the Company. The Shenghe Implied Discount amounted to 36% of that contractually determined gross profit amount. See also Note 4, “Revenue Recognition.” Accounting for the June 2020 Modification As noted above, in June 2020, the Company renegotiated various aspects of its relationship with Shenghe and entered into the Framework Agreement to significantly restructure the aforementioned set of arrangements. Prior to the June 2020 Modification, for accounting purposes, the Original Offtake Agreement constituted a deferred revenue arrangement; however, as a result of the June 2020 Modification, the A&R Offtake Agreement constituted a debt obligation as well as provided for the issuance of the Shenghe Warrant. For further discussion of the deferred revenue arrangement, see Note 4, “Revenue Recognition,” and for further discussion of the debt obligation, see Note 8, “Debt Obligations.” Product Sales and Cost of Sales: The Company and Shenghe enter into separate product sales agreements in which Shenghe purchases all newly-produced material at specified prices. Product sales from these agreements were $59.7 million and $20.6 million for the three months ended March 31, 2021 and 2020, respectively, and are discussed in more detail in Note 4, “Revenue Recognition,” including amounts recognized as deferred revenue. Cost of sales, which includes shipping and freight, related to these agreements with Shenghe was $17.8 million and $12.5 million for the three months ended March 31, 2021 and 2020, respectively. Purchases: The Company purchases reagent products (produced by an unrelated third party manufacturer) used in the flotation process from Shenghe. Total purchases for the three months ended March 31, 2021 and 2020, totaled $0.7 million and $0.3 million, respectively. Royalty Agreement: In April 2017, MPMO entered into a 30-year mineral lease and license agreement with SNR (the “Royalty Agreement”) under which MPMO paid royalties to SNR in the amount of 2.5% of the gross proceeds from the sale of rare earth products made from ores extracted from the Mountain Pass mine, subject to a minimum non-refundable royalty of $0.5 million per year. At the time of entering into the Royalty Agreement, MPMO and SNR had shareholders common to both entities; however, they were not partners in business nor did they hold any other joint interest. In connection with the Business Combination, MPMO and SNR are both wholly-owned subsidiaries of the Company. Consequently, the intercompany transactions between MPMO and SNR after the date of the SNR Mineral Rights Acquisition and the Business Combination eliminate in consolidation, including the effects of the Royalty Agreement. Excluding payments of these minimums (which were treated as a reduction to the obligation), royalty expense was $0.5 million and the Company paid out $0.5 million for the three months ended March 31, 2020. Services Reimbursed: The Company reimbursed JHL Capital Group Holdings for travel-related expenses in the amount of less than $0.1 million during the three months ended March 31, 2021, and $0.1 million during the three months ended March 31, 2020. Accounts Receivable: As of March 31, 2021, and December 31, 2020, $13.8 million and $3.5 million of the accounts receivable, as stated on the unaudited Condensed Consolidated Balance Sheets, were receivable from a related party due to the Company’s sales agreements with Shenghe. Indebtedness: The Company’s related-party debt is described in Note 8, “Debt Obligations.”

SUPPLEMENTAL CASH FLOW INFORMAT

SUPPLEMENTAL CASH FLOW INFORMATION	3 Months Ended
	Mar. 31, 2021
Additional Cash Flow Elements and Supplemental Cash Flow Information [Abstract]
SUPPLEMENTAL CASH FLOW INFORMATION	SUPPLEMENTAL CASH FLOW INFORMATION Supplemental cash flow information and non-cash investing and financing activities were as follows: For the three months ended March 31, (in thousands) 2021 2020 Supplemental cash flow information: Cash paid for interest $ 39 $ 37 Cash refund related to income taxes $ 6 $ — Supplemental non-cash investing and financing activities: Property, plant and equipment acquired with seller-financed equipment notes $ 9,407 $ 889 Property, plant and equipment purchased but not yet paid $ 7,985 $ 360 Finance right-of-use assets obtained in exchange for finance lease liabilities $ 36 $ — Revenue recognized in exchange for debt principal reduction (1) $ 11,276 $ — (1) Of the amount for the three months ended March 31, 2021, $9.2 million pertained to product sales to Shenghe, as discussed in Note 8, “Debt Obligations,” and $2.0 million pertained to the tariff rebate, as discussed in Note 4, “Revenue Recognition. ”

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	3 Months Ended
	Mar. 31, 2021
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On May 4, 2021, the Company announced that it will redeem all of the outstanding Public Warrants to purchase shares of its Common Stock that were issued under the Warrant Agreement, dated April 29, 2020 (the “Warrant Agreement”), by and between the Company and Continental Stock Transfer & Trust Company (“CST”), as warrant agent, for a redemption price of $0.01 per warrant (the “Redemption Price”), that remain outstanding following 5:00 p.m. New York City time on June 7, 2021 (the “Redemption Date”). Under the terms of the Warrant Agreement, the Company is entitled to redeem all of such outstanding Public Warrants if the last sales price of the Common Stock is at least $18.00 per share on each of 20 trading days within a 30-trading day period ending three In addition, in accordance with the Warrant Agreement, the Company’s Board of Directors has elected to require that all Public Warrants are to be exercised only on a “cashless basis.” Accordingly, holders may no longer exercise Public Warrants and receive Common Stock in exchange for payment in cash of the $11.50 per warrant exercise price. Instead, a holder exercising a Public Warrant will be deemed to pay the $11.50 per warrant exercise price by the surrender of 0.3808 of a share of Common Stock that such holder would have been entitled to receive upon a cash exercise of a Public Warrant. Accordingly, by virtue of the cashless exercise of the Public Warrants, exercising warrant holders will receive 0.6192 of a share of Common Stock for each Public Warrant surrendered for exercise. Any Public Warrants that remain unexercised at 5:00 p.m. New York City time on the Redemption Date will be delisted, void and no longer exercisable, and the holders will have no rights with respect to those Public Warrants, except to receive the Redemption Price.

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	The unaudited Condensed Consolidated Financial Statements of the Company have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) for interim financial information and with the rules and regulations of the U.S. Securities and Exchange Commission. Accordingly, they do not include all of the information and notes required by GAAP for complete consolidated financial statements. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation have been included.Results of operations and cash flows for the interim periods presented herein are not necessarily indicative of the results that would be achieved during a full year of operations or in future periods. These unaudited Condensed Consolidated Financial Statements and notes thereto should be read in conjunction with the Consolidated Financial Statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020.
Principles of Consolidation	The unaudited Condensed Consolidated Financial Statements include the accounts of MP Materials Corp. and its subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Concentration of Risk	As of March 31, 2021, Shenghe accounted for more than 90% of product sales. Shenghe, a related party of the Company, has entered into an arrangement to purchase substantially all of the Company’s production, and has previously purchased portions of the Company’s stockpile inventory. While as with any contract there is risk of nonperformance, we do not believe that it is reasonably possible that the agreement will be terminated in the near term as it would significantly delay Shenghe’s recovery of non-interest-bearing advance payments that are recognized by the Company as debt. See Note 3, “Relationship and Agreements with Shenghe,” for additional information. Furthermore, while revenue is generated in the United States, our principal customer is located in China and may transport and sell products in the Chinese market; therefore, the Company’s gross profit is affected by Shenghe’s ultimate realized prices in China. In addition, there is an ongoing economic conflict between China and the United States that has resulted in tariffs and trade barriers that may negatively affect the Company’s business and results of operations. In December 2019, a novel strain of coronavirus (known as “COVID-19”) began to impact the population of China, where our principal customer is located. The outbreak of COVID-19 has grown both in the United States and globally, and related government and private sector responsive actions have adversely affected the global economy, including significant business and supply chain disruption as well as broad-based changes in supply and demand. In December 2019, a series of emergency quarantine measures taken by the Chinese government disrupted domestic business activities in China during the weeks after the initial outbreak of COVID-19. These disruptions have occurred periodically since the start of COVID-19 outbreak as measures intended to impede the spread of the virus have adapted. Since the initial COVID-19 outbreak, many countries, including the United States, have imposed restrictions on travel to and from China and elsewhere, as well as general movement restrictions, business closures and other measures imposed to slow the spread of COVID-19. At the onset of the outbreak, we initially experienced shipping delays due to overseas port slowdowns and container shortages, but we did not experience a reduction in production or sales. However, beginning in the fourth quarter of 2020 and continuing into the first quarter of 2021, we again saw shipping delays and container shortages from congestion at port facilities, which has been exacerbated by COVID-19. Congestion at U.S. and international ports could affect the capacity at ports to receive deliveries of products or the loading of shipments onto vessels. As the situation continues to develop, it is impossible to predict the effect and ultimate impact of the COVID-19 pandemic on the Company’s business and results of operations. While the quarantine, social distancing and other regulatory measures instituted or recommended in response to COVID-19 are expected to be temporary, the duration of the business disruptions, and related financial impact, cannot be estimated at this time.
Use of Estimates	The preparation of the unaudited Condensed Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect (i) the reported amounts of assets and liabilities, (ii) the disclosure of contingent assets and liabilities at the date of the unaudited Condensed Consolidated Financial Statements, and (iii) the reported amounts of revenues and expenses during the reporting period. Accordingly, actual results may differ from those estimates.
Debt Issuance Costs	Debt issuance costs that are incurred by the Company in connection with the issuance of debt are deferred and amortized to interest expense using the effective interest method over the contractual term of the underlying indebtedness. Debt issuance costs reduce the carrying amount of the associated debt.
Recently Issued Accounting Pronouncements	As an “emerging growth company,” the Jumpstart Our Business Startups Act (“JOBS Act”) allows the Company to delay adoption of new or revised accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. The Company has elected to use this extended transition period under the JOBS Act. The adoption dates discussed below reflect this election.In June 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurements of Credit Losses on Financial Instruments” (“ASU 2016-13”), which sets forth a “current expected credit loss” model which requires the Company to measure all expected credit losses for financial instruments held at the reporting date based on historical experience, current conditions, and reasonable supportable forecasts. We elected to early adopt ASU 2016-13 during the first quarter of 2021 using a modified retrospective approach, which did not have a material impact on our unaudited Condensed Consolidated Financial Statements, and did not result in a cumulative-effect adjustment. In August 2018, the FASB issued ASU No. 2018-15, “Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract” (“ASU 2018-15”), which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. ASU 2018-15 requires capitalized costs to be amortized on a straight-line basis generally over the term of the arrangement, and the financial statement presentation for these capitalized costs would be the same as that of the fees related to the hosting arrangements. We elected to early adopt ASU 2018-15 during the first quarter of 2021 using a prospective approach, which did not have a material impact on our unaudited Condensed Consolidated Financial Statements. In August 2020, the FASB issued ASU No. 2020-06, “Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity” (“ASU 2020-06”), which (i) simplifies the accounting for convertible debt instruments and convertible preferred stock by removing the existing guidance in Accounting Standards Codification (“ASC”) Subtopic 470-20, “Debt—Debt with Conversion and Other Options,” that requires entities to account for beneficial conversion features and cash conversion features in equity, separately from the host convertible debt or preferred stock; (ii) revises the scope exception from derivative accounting in ASC Subtopic 815-40, “Derivatives and Hedging—Contracts in Entity’s Own Equity,” for freestanding financial instruments and embedded features that are both indexed to the issuer’s own stock and classified in stockholders’ equity, by removing certain criteria required for equity classification; and (iii) revises the guidance in ASC Topic 260, “Earnings Per Share,” to require entities to calculate diluted earnings per share (“EPS”) for convertible instruments by using the if-converted method. In addition, entities must presume share settlement for purposes of calculating diluted EPS when an instrument may be settled in cash or shares. We elected to early adopt ASU 2020-06 during the first quarter of 2021 using a prospective approach. See Note 8, “Debt Obligations,” for a discussion of our Convertible Notes (as defined in Note 8, “Debt Obligations” ), which we issued on March 26, 2021. A variety of proposed or otherwise potential accounting standards are currently being studied by standard-setting organizations and certain regulatory agencies. Because of the tentative and preliminary nature of such proposed standards, we have not yet determined the effect, if any, that the implementation of such proposed standards would have on our unaudited Condensed Consolidated Financial Statements.

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Contract With Customer Liability, Related Party	Significant activity for the deferred revenue balance (including current portion) was as follows: For the three months ended March 31, (in thousands) 2021 2020 Opening balance (1) $ — $ 35,543 Prepayments received (2) — 1,500 Prepayments on sales (3) — 5,212 Revenue recognized (4) — (2,191) Ending balance $ — $ 40,064 (1) Of the amount for the three months ended March 31, 2020, $6.6 million was classified as current based on when such amount was expected to be realized. (2) Amount for the three months ended March 31, 2020, relates to the contractual commitment for Shenghe to provide funds to the Company (the Initial Prepayment Amount). (3) Amount for the three months ended March 31, 2020, relates to a prepayment made by Shenghe to the Company in advance of recognizing the revenue associated with the sale of products. (4) As discussed above, for sales made to Shenghe during the period from July 2019 through early June 2020, as a result of the Shenghe Implied Discount, we recognized an amount of deferred revenue applicable to such sales equal to 64% of the gross profit realized by Shenghe on sales of this product to its own customers.

RESTRICTED CASH (Tables)

RESTRICTED CASH (Tables)	3 Months Ended
	Mar. 31, 2021
Cash and Cash Equivalents [Abstract]
Restricted cash balances	The Company’s restricted cash balances were as follows: March 31, 2021 December 31, 2020 (in thousands) Restricted cash, current $ 3,765 $ 3,688 Restricted cash, non-current 9,115 9,100 Total restricted cash $ 12,880 $ 12,788

INVENTORIES (Tables)

INVENTORIES (Tables)	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Inventories	The Company’s inventories consisted of the following: March 31, 2021 December 31, 2020 (in thousands) Materials and supplies (1) $ 6,362 $ 5,124 In-process (2) 26,356 24,524 Finished goods (3) 2,380 2,624 Total inventory $ 35,098 $ 32,272 (1) Comprised of raw materials, spare parts, reagent chemicals, and packaging materials used in the production of rare earth products (2) Primarily comprised of mined ore stockpiles and bastnaesite ore in various stages of the production process that are drawn down based on the demands of our mine production plan (3) Primarily comprised of packaged bastnaesite ore that is ready for sale

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Tables)	3 Months Ended
	Mar. 31, 2021
Property, Plant and Equipment [Abstract]
Property, plant and equipment	Property, plant and equipment consisted of the following: March 31, 2021 December 31, 2020 (in thousands) Machinery and equipment $ 33,677 $ 22,911 Buildings 3,147 2,953 Land and land improvements 8,938 6,534 Assets under construction 70,125 46,814 Mineral rights 437,654 437,654 Property, plant and equipment 553,541 516,866 Less: Accumulated depreciation and depletion (21,037) (14,892) Property, plant and equipment, net $ 532,504 $ 501,974

DEBT OBLIGATIONS (Tables)

DEBT OBLIGATIONS (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of debt obligations	The Company’s current and non-current portions of long-term debt were as follows: March 31, 2021 December 31, 2020 (in thousands) Long-term debt Convertible Notes due 2026 $ 690,000 $ — Paycheck Protection Loan 3,364 3,364 Less: Unamortized debt issuance costs (17,677) — Net carrying amount 675,687 3,364 Less: Current installments of long-term debt (3,105) (2,403) Long-term debt, net of current portion $ 672,582 $ 961 Long-term debt to related party Offtake Advances $ 60,401 $ 71,843 Less: Unamortized debt discount (4,211) (5,393) Net carrying amount 56,190 66,450 Less: Current installments of long-term debt to related party (38,457) (22,070) Long-term debt to related party, net of current portion $ 17,733 $ 44,380 The current and non-current portions of the equipment notes, which are included within the unaudited Condensed Consolidated Balance Sheets in “Other current liabilities” and “Other non-current liabilities,” respectively, were as follows: March 31, 2021 December 31, 2020 (in thousands) Equipment notes Current $ 2,614 $ 835 Non-current 8,997 1,267 $ 11,611 $ 2,102
Interest expense, net	Interest expense, net, was as follows: For the three months ended March 31, (in thousands) 2021 2020 Interest expense $ 1,165 $ 803 Capitalized interest (11) — Interest expense, net $ 1,154 $ 803 Interest expense related to the Convertible Notes was as follows: For the three months ended March 31, (in thousands) 2021 2020 Coupon interest $ 24 $ — Amortization of debt issuance costs 48 — Convertible Notes interest expense $ 72 $ —

LEASE OBLIGATIONS (Tables)

LEASE OBLIGATIONS (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Supplemental disclosure for the Consolidated Balance Sheets related to operating and finance leases	Supplemental disclosure for the unaudited Condensed Consolidated Balance Sheets related to the Company’s operating and finance leases is as follows: Location on Unaudited Condensed Consolidated Balance Sheets March 31, 2021 December 31, 2020 (in thousands) Operating Leases: Right-of-use assets Other non-current assets $ 579 $ 1,090 Operating lease liability, current Other current liabilities $ 333 $ 761 Operating lease liability, non-current Other non-current liabilities 271 357 Total operating lease liabilities $ 604 $ 1,118 Finance Leases: Right-of-use assets Finance lease right-of-use assets $ 974 $ 1,028 Finance lease liability, current Current portion of finance lease liabilities $ 279 $ 266 Finance lease liability, non-current Finance lease liabilities, net of current portion 687 736 Total finance lease liabilities $ 966 $ 1,002

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value Measurements, Carrying Amounts and Estimated Fair Values by Input Level	The carrying amounts and estimated fair values by input level of the Company’s financial instruments were as follows: March 31, 2021 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 1,181,515 $ 1,181,515 $ 1,181,515 $ — $ — Restricted cash $ 12,880 $ 12,880 $ 12,880 $ — $ — Financial liabilities: Convertible Notes $ 672,323 $ 711,882 $ 711,882 $ — $ — Offtake Advances $ 56,190 $ 58,462 $ — $ — $ 58,462 Equipment notes $ 11,611 $ 11,210 $ — $ 11,210 $ — December 31, 2020 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 519,652 $ 519,652 $ 519,652 $ — $ — Restricted cash $ 12,788 $ 12,788 $ 12,788 $ — $ — Financial liabilities: Offtake Advances $ 66,450 $ 68,151 $ — $ — $ 68,151 Equipment notes $ 2,102 $ 2,077 $ — $ 2,077 $ —

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of weighted-average common shares outstanding used in the calculation of basic earnings per share to the weighted-average common shares outstanding used in the calculation of diluted earnings per share	The following table reconciles the weighted-average common shares outstanding used in the calculation of basic EPS to the weighted-average common shares outstanding used in the calculation of diluted EPS: For the three months ended March 31, 2021 2020 Weighted-average shares outstanding, basic 168,922,566 66,556,975 Assumed conversion of Public Warrants 7,922,357 — Assumed conversion of Convertible Notes 1,038,961 — Assumed conversion of restricted stock 1,176,133 — Assumed conversion of restricted stock units 259,472 — Weighted-average shares outstanding, diluted 179,319,489 66,556,975
Schedule of the calculation of basic and diluted earnings per share	The following table presents the calculation of basic and diluted EPS for the Company’s Common Stock: For the three months ended March 31, (in thousands, except share and per share data) 2021 2020 Calculation of basic EPS: Net income $ 16,119 $ 1,925 Weighted-average shares outstanding, basic 168,922,566 66,556,975 Basic EPS $ 0.10 $ 0.03 Calculation of diluted EPS: Net income $ 16,119 $ 1,925 Interest expense, net of tax (1) : Convertible Notes 57 — Diluted income $ 16,176 $ 1,925 Weighted-average shares outstanding, diluted 179,319,489 66,556,975 Diluted EPS $ 0.09 $ 0.03 (1) The three months ended March 31, 2021, was tax-effected at a rate of 21.8%. As discussed in Note 8, “Debt Obligations,” the Convertible Notes were issued in March 2021; therefore, no adjustment is required for the three months ended March 31, 2020.

SUPPLEMENTAL CASH FLOW INFORM_2

SUPPLEMENTAL CASH FLOW INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2021
Additional Cash Flow Elements and Supplemental Cash Flow Information [Abstract]
Schedule of Cash Flow, Supplemental Disclosures	Supplemental cash flow information and non-cash investing and financing activities were as follows: For the three months ended March 31, (in thousands) 2021 2020 Supplemental cash flow information: Cash paid for interest $ 39 $ 37 Cash refund related to income taxes $ 6 $ — Supplemental non-cash investing and financing activities: Property, plant and equipment acquired with seller-financed equipment notes $ 9,407 $ 889 Property, plant and equipment purchased but not yet paid $ 7,985 $ 360 Finance right-of-use assets obtained in exchange for finance lease liabilities $ 36 $ — Revenue recognized in exchange for debt principal reduction (1) $ 11,276 $ — (1) Of the amount for the three months ended March 31, 2021, $9.2 million pertained to product sales to Shenghe, as discussed in Note 8, “Debt Obligations,” and $2.0 million pertained to the tariff rebate, as discussed in

DESCRIPTION OF BUSINESS AND B_2

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Details)	3 Months Ended
	Mar. 31, 2021segment$ / shares	Dec. 31, 2020$ / shares	Nov. 17, 2020$ / shares
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Common stock, par value (usd per share) | $ / shares	$ 0.0001	$ 0.0001	$ 0.0001
Number of reportable segments | segment	1

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Concentration Risk [Line Items]
Allowance for credit losses	$ 0	$ 0
Shenghe | Product sales | Customer concentration risk | Shenghe
Concentration Risk [Line Items]
Concentration risk percentage	90.00%

RELATIONSHIP AND AGREEMENTS W_2

RELATIONSHIP AND AGREEMENTS WITH SHENGHE - Original Commercial Agreements (Details) - Affiliated Entity - USD ($) $ in Millions	Jun. 20, 2017	May 31, 2017
Initial Prepayment Amount
Related Party Transaction [Line Items]
Advances		$ 50
Increase in advances	$ 30
First Additional Advance
Related Party Transaction [Line Items]
Advances	$ 30

RELATIONSHIP AND AGREEMENTS W_3

RELATIONSHIP AND AGREEMENTS WITH SHENGHE - Framework Agreement and Restructured Commercial Arrangements (Details) - Affiliated Entity - USD ($) $ in Millions	Jun. 05, 2020	Jun. 20, 2017	May 31, 2017
Original Offtake Agreement, Second Additional Advance | Shenghe
Related Party Transaction [Line Items]
Advances	$ 35.5
Initial Prepayment Amount
Related Party Transaction [Line Items]
Advances			$ 50
Increase in advances		$ 30
Initial Prepayment Amount | Shenghe
Related Party Transaction [Line Items]
Increase in advances	$ 30	$ 30

RELATIONSHIP AND AGREEMENTS W_4

RELATIONSHIP AND AGREEMENTS WITH SHENGHE - Activity Related to Modifications (Details) - Affiliated Entity - USD ($) $ in Millions	Jun. 05, 2020	Jun. 20, 2017	May 31, 2017
First Additional Advance
Related Party Transaction [Line Items]
Advances		$ 30
Initial Prepayment Amount
Related Party Transaction [Line Items]
Advances			$ 50
Increase in advances		30
Shenghe | First Additional Advance
Related Party Transaction [Line Items]
Advances		30
Debt fair value		26.5
Deferred revenue arrangement modification fair value		3.5
Preferred interest, fair value		2.3
Shenghe | Initial Prepayment Amount
Related Party Transaction [Line Items]
Increase in advances	$ 30	$ 30
Shenghe | Shenghe Implied Discount
Related Party Transaction [Line Items]
Shenghe Implied Discount, percentage of contractual gross profit		36.00%

REVENUE RECOGNITION - Additiona

REVENUE RECOGNITION - Additional Information (Details) - USD ($) $ in Thousands	Jun. 20, 2017	Mar. 31, 2021	Mar. 31, 2020	Jun. 05, 2020
Related Party Transaction [Line Items]
Prepayments received		$ 0	$ 1,500
Affiliated Entity | Shenghe
Related Party Transaction [Line Items]
Deferred revenue percentage recognized from gross profit	64.00%
Affiliated Entity | Shenghe | Shenghe Implied Discount
Related Party Transaction [Line Items]
Shenghe Implied Discount, percentage of contractual gross profit	36.00%
Affiliated Entity | Shenghe | First Additional Advance
Related Party Transaction [Line Items]
Preferred interest, fair value	$ 2,300
Affiliated Entity | Shenghe | Minimum | Shenge Sales Discount
Related Party Transaction [Line Items]
Related parties, sales discount				3.00%
Affiliated Entity | Shenghe | Maximum | Shenge Sales Discount
Related Party Transaction [Line Items]
Related parties, sales discount				6.00%

REVENUE RECOGNITION - Significa

REVENUE RECOGNITION - Significant Activity For Deferred Revenue (Details) - USD ($) $ in Thousands	Jun. 20, 2017	Mar. 31, 2021	Mar. 31, 2020
Contract With Customer, Liability, Related Parties [Rollforward]
Opening balance		$ 0	$ 35,543
Prepayments received		0	1,500
Prepayments on sales		0	5,212
Revenue recognized		0	(2,191)
Ending balance		$ 0	40,064
Deferred revenue- related parties			$ 6,600
Affiliated Entity | Shenghe
Contract With Customer, Liability, Related Parties [Rollforward]
Deferred revenue percentage recognized from gross profit	64.00%

RESTRICTED CASH (Details)

RESTRICTED CASH (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Cash and Cash Equivalents [Abstract]
Restricted cash, current	$ 3,765	$ 3,688	$ 34
Restricted cash, non-current	9,115	9,100	$ 27,066
Total restricted cash	$ 12,880	$ 12,788

INVENTORIES (Details)

INVENTORIES (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Materials and supplies	$ 6,362	$ 5,124
In-process	26,356	24,524
Finished goods	2,380	2,624
Total inventory	$ 35,098	$ 32,272

PROPERTY, PLANT AND EQUIPMENT -

PROPERTY, PLANT AND EQUIPMENT - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended
	Feb. 28, 2021	Mar. 31, 2021	Mar. 31, 2020
Property, Plant and Equipment [Abstract]
Capitalized expenditures		$ 27,300,000	$ 1,000,000
Interest capitalized		11,000	0
Depreciation expense		1,500,000	1,200,000
Depletion expense		4,500,000	100,000
Asset impairment charges		0	0
Additions of property, plant and equipment	$ 9,400,000	$ 19,298,000	$ 618,000

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT - Schedule (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 553,541	$ 516,866
Less: Accumulated depreciation and depletion	(21,037)	(14,892)
Property, plant and equipment, net	532,504	501,974
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment	33,677	22,911
Buildings
Property, Plant and Equipment [Line Items]
Property, plant and equipment	3,147	2,953
Land and land improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment	8,938	6,534
Assets under construction
Property, Plant and Equipment [Line Items]
Property, plant and equipment	70,125	46,814
Mineral rights
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 437,654	$ 437,654

DEBT OBLIGATIONS - Schedule of

DEBT OBLIGATIONS - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020
Debt Instrument [Line Items]
Less: Unamortized debt issuance costs	$ (17,677)	$ 0
Net carrying amount	675,687	3,364
Less: Current installments of long-term debt to related party	(3,105)	(2,403)
Long-term debt to related party, net of current portion	672,582	961
Related Party Debt
Debt Instrument [Line Items]
Less: Unamortized debt discount	(4,211)	(5,393)
Net carrying amount	56,190	66,450
Less: Current installments of long-term debt to related party	(38,457)	(22,070)
Long-term debt to related party, net of current portion	17,733	44,380
Convertible Debt | Convertible Notes Due 2026
Debt Instrument [Line Items]
Outstanding balance, gross	690,000	0
Less: Unamortized debt issuance costs	(17,700)
Net carrying amount	672,300
Paycheck Protection Loan | Paycheck Protection Program Loan
Debt Instrument [Line Items]
Outstanding balance, gross	3,364	3,364
Offtake Advances | Related Party Debt
Debt Instrument [Line Items]
Outstanding balance, gross	60,401	71,843	$ 94,000
Less: Unamortized debt discount			$ (8,300)
Less: Current installments of long-term debt to related party	$ (42,500)	$ (25,700)

DEBT OBLIGATIONS - Convertible

DEBT OBLIGATIONS - Convertible Notes (Details) $ / shares in Units, $ in Thousands	Mar. 26, 2021USD ($)d$ / shares	Mar. 31, 2021USD ($)shares	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
Debt issuance costs		$ 17,677	$ 0
Net carrying amount		$ 675,687	3,364
Convertible Debt | Convertible Notes Due 2026
Debt Instrument [Line Items]
Debt instrument, face amount	$ 690,000
Interest rate	0.25%
Debt issuance costs	$ 17,400
Debt instrument, convertible, conversion price (in dollars per share) | $ / shares	$ 44.28
Debt instrument, convertible, conversion ratio	0.0225861
Debt instrument, convertible, number of equity instruments (in shares) | shares		19,714,266
Debt Instrument, convertible, if-converted value in excess of principal		$ 18,700
Debt instrument, redemption price, percentage	100.00%
Outstanding balance, gross		690,000	$ 0
Debt issuance costs		17,700
Net carrying amount		$ 672,300
Effective interest rate		0.51%
Debt term		5 years
Convertible Debt | Convertible Notes Due 2026 | Maximum
Debt Instrument [Line Items]
Debt instrument, convertible, conversion ratio	0.0285714
Convertible Debt | Convertible Notes Due 2026 | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Debt instrument, convertible, threshold trading days | d	20
Threshold consecutive trading days | d	30
Debt instrument, convertible, threshold percentage of stock price trigger	130.00%
Number of business days in which debt can be converted | d	5
Consecutive business days | d	5
Convertible Debt | Convertible Notes Due 2026 | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Debt instrument, convertible, percentage of product of the last reported sale price of the company’s common stock and the conversion rate on each such trading day	98.00%

DEBT OBLIGATIONS - Paycheck Pro

DEBT OBLIGATIONS - Paycheck Protection Loan (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2020	Mar. 31, 2021	Mar. 31, 2020
Debt Instrument [Line Items]
Proceeds from debt issuance		$ 690,000	$ 0
Paycheck Protection Loan | Paycheck Protection Program Loan
Debt Instrument [Line Items]
Proceeds from debt issuance	$ 3,400

DEBT OBLIGATIONS - Offtake Adva

DEBT OBLIGATIONS - Offtake Advances (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Jan. 31, 2021	Jun. 30, 2020	Mar. 31, 2021	Apr. 01, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Current portion of debt			$ 3,105		$ 2,403
Shenghe
Debt Instrument [Line Items]
Rebate income	$ 2,200
Related Party Debt
Debt Instrument [Line Items]
Debt discount			4,211		5,393
Current portion of debt			38,457		22,070
Related Party Debt | Offtake Advances
Debt Instrument [Line Items]
Required payments, percent of net profits from sales of assets		100.00%
Required payments, percent of net income		100.00%
Reduction in debt as a result of sales			9,200
Outstanding balance, gross		$ 94,000	$ 60,401		71,843
Debt discount		8,300
Debt term			2 years
Current portion of debt			$ 42,500		$ 25,700
Reduction in debt principal due to change in price estimates			2,200
Reduction in debt discount due to change in price estimates			$ 200
Related Party Debt | Offtake Advances | Subsequent event
Debt Instrument [Line Items]
Effective interest rate				10.37%
Related Party Debt | Offtake Advances | Minimum
Debt Instrument [Line Items]
Effective interest rate			4.41%
Related Party Debt | Offtake Advances | Maximum
Debt Instrument [Line Items]
Effective interest rate			6.59%
Second Offtake Advance | Offtake Advances
Debt Instrument [Line Items]
Advance funded		$ 35,500

DEBT OBLIGATIONS - Equipment No

DEBT OBLIGATIONS - Equipment Notes (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Feb. 28, 2021	Mar. 31, 2021	Dec. 31, 2020
Equipment notes
Current		$ 3,105	$ 2,403
Non-current		672,582	961
Net carrying amount		675,687	3,364
Equipment notes
Debt Instrument [Line Items]
Debt term	5 years
Interest rate	4.50%
Advance funded	$ 9,700
Equipment notes
Current		2,614	835
Non-current		8,997	1,267
Net carrying amount		$ 11,611	$ 2,102
Equipment notes | Minimum
Debt Instrument [Line Items]
Debt term		4 years
Interest rate		0.00%
Equipment notes | Maximum
Debt Instrument [Line Items]
Debt term		5 years
Interest rate		6.50%

DEBT OBLIGATIONS - Interest Exp

DEBT OBLIGATIONS - Interest Expense, Net (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Debt Instrument [Line Items]
Interest expense	$ 1,165,000	$ 803,000
Capitalized interest	(11,000)	0
Interest expense, net	1,154,000	803,000
Convertible Debt | Convertible Notes Due 2026
Debt Instrument [Line Items]
Interest expense	72,000	0
Coupon interest	24,000	0
Amortization of debt issuance costs	$ 48,000	$ 0

LEASE OBLIGATIONS - Supplementa

LEASE OBLIGATIONS - Supplemental Disclosure for the Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Operating Leases:
Right-of-use assets	$ 579	$ 1,090
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other non-current assets	Other non-current assets
Operating lease liability, current	$ 333	$ 761
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities	Other current liabilities
Operating lease liability, non-current	$ 271	$ 357
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other non-current liabilities	Other non-current liabilities
Total operating lease liabilities	$ 604	$ 1,118
Finance Leases:
Right-of-use assets	974	1,028
Finance lease liability, current	279	266
Finance lease liabilities, net of current portion	687	736
Total finance lease liabilities	$ 966	$ 1,002

ASSET RETIREMENT AND ENVIRONM_2

ASSET RETIREMENT AND ENVIRONMENTAL OBLIGATIONS - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Unusual Risk or Uncertainty [Line Items]
Asset retirement obligation, current	$ 0.1	$ 0.1
Estimated undiscounted cash flows, to satisfy obligation	141.6	142.3
Closure and reclamation obligations, financial assurances	$ 38.5	38.4
Remediation term	27 years
Discount rate	2.93%
Environmental obligations, undiscounted cost	$ 28	28.2
Environmental obligations, current	$ 0.5	$ 0.5
Minimum
Unusual Risk or Uncertainty [Line Items]
Asset retirement obligations, credit-adjusted risk free rate	7.10%
Maximum
Unusual Risk or Uncertainty [Line Items]
Asset retirement obligations, credit-adjusted risk free rate	8.20%

INCOME TAXES - Additional Infor

INCOME TAXES - Additional Information (Details)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Effective tax rate	21.80%	0.00%

STOCKHOLDERS_ EQUITY (Details)

STOCKHOLDERS’ EQUITY (Details) - $ / shares	May 04, 2021	May 04, 2020	Mar. 31, 2021	Dec. 31, 2020	Nov. 17, 2020	Nov. 16, 2020
Class of Warrant or Right [Line Items]
Capital stock, authorized (shares)					500,000,000	221,000,000
Common stock, authorized (shares)			450,000,000	450,000,000	450,000,000
Preferred stock, authorized (shares)			50,000,000	50,000,000	50,000,000
Common stock, par value (usd per share)			$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, par value (usd per share)			$ 0.0001	$ 0.0001	$ 0.0001
Public Warrant
Class of Warrant or Right [Line Items]
Number of securities called by warrants (in shares)		11,499,968
Exercise price of warrants (usd per share)		$ 11.50
Period after which warrants become exercisable		12 months
Warrants expiration period		5 years
Public Warrant | Subsequent event
Class of Warrant or Right [Line Items]
Exercise price of warrants (usd per share)	$ 11.50
Warrant redemption requirement, stock price (usd per share)	$ 18
Warrant redemption requirement, trading days threshold	20 days
Warrant redemption requirement, trading day period	30 days
Warrant redemption requirement, days before sending notice of redemption to warrant holders	3 days
Warrant redemption price (usd per share)	$ 0.01
Redemption period minimum written days' notice	30 days

STOCK-BASED COMPENSATION - Addi

STOCK-BASED COMPENSATION - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5.7	$ 0
2020 Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants (in shares)	7,160,148

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Recurring | Level 1
Financial assets:
Cash and cash equivalents	$ 1,181,515	$ 519,652
Restricted cash	12,880	12,788
Fair Value, Recurring | Level 2
Financial assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Fair Value, Recurring | Level 3
Financial assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Convertible Notes | Fair Value, Recurring | Level 1
Financial liabilities:
Debt fair value	711,882
Convertible Notes | Fair Value, Recurring | Level 2
Financial liabilities:
Debt fair value	0
Convertible Notes | Fair Value, Recurring | Level 3
Financial liabilities:
Debt fair value	0
Offtake Advances | Fair Value, Recurring | Level 1
Financial liabilities:
Debt fair value	0	0
Offtake Advances | Fair Value, Recurring | Level 2
Financial liabilities:
Debt fair value	0	0
Offtake Advances | Fair Value, Recurring | Level 3
Financial liabilities:
Debt fair value	58,462	68,151
Equipment notes | Fair Value, Recurring | Level 1
Financial liabilities:
Debt fair value	0	0
Equipment notes | Fair Value, Recurring | Level 2
Financial liabilities:
Debt fair value	11,210	2,077
Equipment notes | Fair Value, Recurring | Level 3
Financial liabilities:
Debt fair value	0	0
Carrying Amount
Financial assets:
Cash and cash equivalents	1,181,515	519,652
Restricted cash	12,880	12,788
Carrying Amount | Convertible Notes
Financial liabilities:
Debt fair value	672,323
Carrying Amount | Offtake Advances
Financial liabilities:
Debt fair value	56,190	66,450
Carrying Amount | Equipment notes
Financial liabilities:
Debt fair value	11,611	2,102
Fair Value | Fair Value, Recurring
Financial assets:
Cash and cash equivalents	1,181,515	519,652
Restricted cash	12,880	12,788
Fair Value | Convertible Notes | Fair Value, Recurring
Financial liabilities:
Debt fair value	711,882
Fair Value | Offtake Advances | Fair Value, Recurring
Financial liabilities:
Debt fair value	58,462	68,151
Fair Value | Equipment notes | Fair Value, Recurring
Financial liabilities:
Debt fair value	$ 11,210	$ 2,077

EARNINGS PER SHARE - Schedule o

EARNINGS PER SHARE - Schedule of Weighted Average Number of Shares (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Class of Warrant or Right [Line Items]
Basic (in shares)	168,922,566	66,556,975
Assumed conversion of Public Warrants	7,922,357	0
Assumed conversion of Convertible Notes	1,038,961	0
Diluted (in shares)	179,319,489	66,556,975
Restricted Stock
Class of Warrant or Right [Line Items]
Assumed conversion of restricted stock awards	1,176,133	0
Restricted Stock Units (RSUs)
Class of Warrant or Right [Line Items]
Assumed conversion of restricted stock awards	259,472	0

EARNINGS PER SHARE - Calculatio

EARNINGS PER SHARE - Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Calculation of basic EPS:
Net income	$ 16,119	$ 1,925
Basic (in shares)	168,922,566	66,556,975
Basic (in USD per share)	$ 0.10	$ 0.03
Calculation of diluted EPS:
Interest expense on convertible debt, net of tax	$ 57	$ 0
Diluted income	$ 16,176	$ 1,925
Diluted (in shares)	179,319,489	66,556,975
Diluted (in USD per share)	$ 0.09	$ 0.03
Effective tax rate	21.80%	0.00%

RELATED PARTY TRANSACTIONS (Det

RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Apr. 30, 2017	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Royalty expense to SNR		$ 0	$ 487
Accounts receivable (including related party), net of allowance for credit losses of $0 and $0, respectively		13,925		$ 3,589
Finance right-of-use assets obtained in exchange for finance lease liabilities		36	0
Affiliated Entity
Related Party Transaction [Line Items]
Revenue from related parties		59,700	20,600
Purchases from related party		700	300
Accounts receivable (including related party), net of allowance for credit losses of $0 and $0, respectively		13,800		$ 3,500
Affiliated Entity | Shipping And Freight Related Agreements With Shenghe
Related Party Transaction [Line Items]
Expenses from transactions with related party		17,800	12,500
Affiliated Entity | Travel-Related Expenses | JHL Capital Group Holdings
Related Party Transaction [Line Items]
Expenses from transactions with related party		$ 100	100
MPMO | Royalty Agreement With SNR
Related Party Transaction [Line Items]
Royalty Agreement, term	30 days
Royalty interest percentage	2.50%
Related party transaction, minimum non-refundable annual royalty payable	$ 500
Royalty expense to SNR			500
Payments for royalties			$ 500

SUPPLEMENTAL CASH FLOW INFORM_3

SUPPLEMENTAL CASH FLOW INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Supplemental cash flow information:
Cash paid for interest	$ 39	$ 37
Cash refund related to income taxes	6	0
Supplemental non-cash investing and financing activities:
Property, plant and equipment acquired with seller-financed equipment notes	9,407	889
Property, plant and equipment purchased but not yet paid	7,985	360
Finance right-of-use assets obtained in exchange for finance lease liabilities	36	0
Revenue recognized in exchange for debt principal reduction	11,276	$ 0
Offtake Advances | Shenghe | Affiliated Entity
Supplemental non-cash investing and financing activities:
Reduction in principal debt balance due to tariff rebate	2,000
Offtake Advances | Related Party Debt
Supplemental non-cash investing and financing activities:
Reduction in debt as a result of sales	$ 9,200

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - $ / shares	May 04, 2021	May 04, 2020
Public Warrant
Subsequent Event [Line Items]
Exercise price of warrants (usd per share)		$ 11.50
Subsequent event | Public Warrant
Subsequent Event [Line Items]
Class of warrant or right, redemption price per share (usd per share)	$ 0.01
Warrant redemption requirement, stock price (usd per share)	$ 18
Warrant redemption requirement, trading days threshold	20 days
Warrant redemption requirement, trading day period	30 days
Warrant redemption requirement, days before sending notice of redemption to warrant holders	3 days
Exercise price of warrants (usd per share)	$ 11.50
The shares surrendered per warrant for a cashless exercise of the public warrants	0.3808
Subsequent event | Cashless Exercise Of Public Warrants
Subsequent Event [Line Items]
The shares received per warrant for the cashless exercise of the public warrants	0.6192