MP Materials (MP) 10-Q 3 Nov 23 2023 Q3 Quarterly report Financial data

COVER

COVER - shares	9 Months Ended
	Sep. 30, 2023	Oct. 31, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
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	1700 S. Pavilion Center Drive, Suite 800
Entity Address, City or Town	Las Vegas
Entity Address, State or Province	NV
Entity Address, Postal Zip Code	89135
City Area Code	702
Local Phone Number	844-6111
Title of 12(b) Security	Common Stock, par value of $0.0001 per share
Trading Symbol	MP
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		177,815,058
Amendment Flag	false
Entity Central Index Key	0001801368
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 547,668	$ 136,627
Short-term investments	536,994	1,045,718
Total cash, cash equivalents and short-term investments	1,084,662	1,182,345
Accounts receivable (including related party), net of allowance for credit losses of $0 and $0, respectively	13,180	32,856
Inventories	77,179	57,554
Income taxes receivable	4,128	2,201
Prepaid expenses and other current assets	9,162	18,872
Total current assets	1,188,311	1,293,828
Non-current assets
Property, plant and equipment, net	1,097,727	935,743
Operating lease right-of-use assets	10,346	99
Inventories	12,589	5,744
Intangible assets, net	9,179	89
Other non-current assets	4,070	2,284
Total non-current assets	1,133,911	943,959
Total assets	2,322,222	2,237,787
Current liabilities
Accounts payable, construction payables and accrued liabilities	92,096	72,265
Income taxes payable	0	21,163
Operating lease liabilities	728	84
Other current liabilities	4,188	3,969
Total current liabilities	97,012	97,481
Non-current liabilities
Asset retirement obligations	5,462	5,295
Environmental obligations	16,554	16,580
Long-term debt, net	681,094	678,444
Operating lease liabilities	7,014	15
Deferred income taxes	135,435	122,353
Other non-current liabilities	3,578	4,985
Total non-current liabilities	849,137	827,672
Total liabilities	946,149	925,153
Commitments and contingencies (Note 11)
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, 177,802,600 and 177,706,608 shares issued and outstanding, as of September 30, 2023, and December 31, 2022, respectively)	17	18
Additional paid-in capital	974,103	951,008
Retained earnings	401,985	361,419
Accumulated other comprehensive income (loss)	(32)	189
Total stockholders’ equity	1,376,073	1,312,634
Total liabilities and stockholders’ equity	$ 2,322,222	$ 2,237,787

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Allowance for credit losses	$ 0	$ 0
Preferred stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Preferred stock, authorized (in shares)	50,000,000	50,000,000
Preferred stock, issued (in shares)	0	0
Preferred shares, outstanding (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Common stock, authorized (in shares)	450,000,000	450,000,000
Common stock, outstanding (in shares)	177,802,600	177,706,608
Common stock, issued (in shares)	177,802,600	177,706,608

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Total revenue	$ 52,516	$ 124,445	$ 212,240	$ 434,265
Operating costs and expenses:
Cost of sales (including related party)(excluding depreciation, depletion and amortization)	22,217	22,417	69,137	67,682
Selling, general and administrative	19,561	17,722	57,829	56,150
Advanced projects, start-up, development and other	10,209	2,625	25,711	6,212
Depreciation, depletion and amortization	16,751	2,096	37,076	12,763
Accretion of asset retirement and environmental obligations	227	418	681	1,255
Loss on disposals of long-lived assets, net	1,087	0	5,897	258
Total operating costs and expenses	70,052	45,278	196,331	144,320
Operating income (loss)	(17,536)	79,167	15,909	289,945
Interest expense, net	(1,396)	(1,224)	(4,147)	(4,455)
Other income, net	14,456	6,168	41,970	8,574
Income (loss) before income taxes	(4,476)	84,111	53,732	294,064
Income tax benefit (expense)	200	(20,934)	(13,166)	(72,067)
Net income (loss)	$ (4,276)	$ 63,177	$ 40,566	$ 221,997
Earnings (loss) per share:
Basic EPS (in USD per share)	$ (0.02)	$ 0.36	$ 0.23	$ 1.26
Diluted (in USD per share)	$ (0.02)	$ 0.33	$ 0.22	$ 1.16
Weighted-average shares outstanding:
Basic (in shares)	177,231,717	176,543,624	177,034,068	176,476,276
Diluted (in shares)	177,231,717	193,409,857	193,632,662	193,438,939
Rare earth concentrate (including related party)
Total revenue	$ 52,472	$ 124,231	$ 212,139	$ 425,169
Other rare earth products (including related party)
Total revenue	$ 44	$ 214	$ 101	$ 9,096

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (4,276)	$ 63,177	$ 40,566	$ 221,997
Other comprehensive income (loss), net of tax:
Change in net unrealized gains (losses) on available-for-sale securities	134	319	(221)	(97)
Total comprehensive income (loss)	$ (4,142)	$ 63,496	$ 40,345	$ 221,900

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2021		0	177,816,554
Beginning balance at Dec. 31, 2021	$ 1,008,732	$ 0	$ 18	$ 936,299	$ 72,415	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)			60,691
Stock-based compensation	25,970			25,970
Shares used to settle payroll tax withholding (in shares)			(342,607)
Shares used to settle payroll tax withholding	(14,296)			(14,296)
Net income (loss)	221,997				221,997
Unrealized gains (losses) on available-for-sale securities	(97)					(97)
Ending balance (in shares) at Sep. 30, 2022		0	177,534,638
Ending balance at Sep. 30, 2022	1,242,306	$ 0	$ 18	947,973	294,412	(97)
Beginning balance (in shares) at Jun. 30, 2022		0	177,534,132
Beginning balance at Jun. 30, 2022	1,170,737	$ 0	$ 18	939,900	231,235	(416)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)			506
Stock-based compensation	8,073			8,073
Net income (loss)	63,177				63,177
Unrealized gains (losses) on available-for-sale securities	319					319
Ending balance (in shares) at Sep. 30, 2022		0	177,534,638
Ending balance at Sep. 30, 2022	1,242,306	$ 0	$ 18	947,973	294,412	(97)
Beginning balance (in shares) at Dec. 31, 2022		0	177,706,608
Beginning balance at Dec. 31, 2022	1,312,634	$ 0	$ 18	951,008	361,419	189
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)			149,922
Stock-based compensation	20,607			20,607
Shares used to settle payroll tax withholding (in shares)			(206,434)
Shares used to settle payroll tax withholding	(6,476)		$ (1)	(6,475)
Common stock issued to acquire intangible asset (in share)			152,504
Common stock issued to acquire intangible asset	8,963			8,963
Net income (loss)	40,566				40,566
Unrealized gains (losses) on available-for-sale securities	(221)					(221)
Ending balance (in shares) at Sep. 30, 2023		0	177,802,600
Ending balance at Sep. 30, 2023	1,376,073	$ 0	$ 17	974,103	401,985	(32)
Beginning balance (in shares) at Jun. 30, 2023		0	177,626,668
Beginning balance at Jun. 30, 2023	1,364,931	$ 0	$ 17	958,819	406,261	(166)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation (in shares)			37,236
Stock-based compensation	6,665			6,665
Shares used to settle payroll tax withholding (in shares)			(13,808)
Shares used to settle payroll tax withholding	(344)			(344)
Common stock issued to acquire intangible asset (in share)			152,504
Common stock issued to acquire intangible asset	8,963			8,963
Net income (loss)	(4,276)				(4,276)
Unrealized gains (losses) on available-for-sale securities	134					134
Ending balance (in shares) at Sep. 30, 2023		0	177,802,600
Ending balance at Sep. 30, 2023	$ 1,376,073	$ 0	$ 17	$ 974,103	$ 401,985	$ (32)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating activities:
Net income	$ (4,276)	$ 63,177	$ 40,566	$ 221,997
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	16,751	2,096	37,076	12,763
Accretion of asset retirement and environmental obligations	227	418	681	1,255
Accretion of discount on short-term investments			(17,334)	(3,921)
Loss on disposals of long-lived assets, net			410	258
Stock-based compensation expense			19,041	25,019
Accretion of debt discount and amortization of debt issuance costs			2,650	3,153
Revenue recognized in exchange for debt principal reduction			0	(13,566)
Deferred income taxes			13,156	62,561
Decrease (increase) in operating assets:
Accounts receivable (including related party)			19,676	34,991
Inventories			(25,498)	(22,386)
Income taxes receivable			(1,927)	(3,857)
Prepaid expenses, other current and non-current assets			490	1,339
Increase (decrease) in operating liabilities:
Accounts payable and accrued liabilities			8,601	(1,271)
Income taxes payable			(21,163)	(3,463)
Other current and non-current liabilities			55	(453)
Net cash provided by operating activities			76,480	314,419
Investing activities:
Additions to property, plant and equipment			(188,927)	(214,332)
Purchases of short-term investments			(705,241)	(1,358,390)
Proceeds from sales of short-term investments			461,042	313,865
Proceeds from maturities of short-term investments			769,907	212,000
Proceeds from government awards used for construction			1,050	5,130
Net cash provided by (used in) investing activities			337,831	(1,041,727)
Financing activities:
Principal payments on debt obligations and finance leases			(2,101)	(5,139)
Tax withholding on stock-based awards			(6,476)	(14,296)
Net cash used in financing activities			(8,577)	(19,435)
Net change in cash, cash equivalents and restricted cash			405,734	(746,743)
Cash, cash equivalents and restricted cash beginning balance			143,509	1,181,157
Cash, cash equivalents and restricted cash ending balance	549,243	434,414	549,243	434,414
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	547,668	427,969	547,668	427,969
Restricted cash, current	1,228	5,915	1,228	5,915
Restricted cash, non-current	347	530	347	530
Total cash, cash equivalents and restricted cash	$ 549,243	$ 434,414	$ 549,243	$ 434,414

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2023
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: MP Materials Corp., including its subsidiaries (the “Company” or “MP Materials”), is the largest producer of rare earth materials in the Western Hemisphere. The Company, which is headquartered in Las Vegas, Nevada, owns and operates the Mountain Pass Rare Earth Mine and Processing Facility (“Mountain Pass”), the only rare earth mining and processing site of scale in North America, and is constructing a rare earth metal, alloy and magnet manufacturing facility in Fort Worth, Texas (the “Fort Worth Facility”), where the Company anticipates manufacturing, among other products, neodymium-iron-boron (“NdFeB”) permanent magnets. Currently, the Company primarily produces a rare earth concentrate that is principally sold pursuant to the Offtake Agreement to Shenghe (as such terms are defined in Note 15 , “Related-Party Transactions ,” ), a related party of the Company, that, in turn, typically sells that product to refiners in China. These refiners separate the constituent rare earth elements contained within the concentrate and sell the separated products to their customers. Upon completing initial commissioning of the remaining circuits of the Company’s Stage II optimization project (“Stage II”) in the third quarter of 2023, the Company began producing separated rare earth products, including neodymium-praseodymium (“NdPr”) oxide. The Company anticipates selling these new products to customers in the U.S. and around the globe beginning in the fourth quarter of 2023, including to Japanese customers pursuant to a distributorship agreement with Sumitomo Corporation of Americas (“Sumitomo”). Additionally, in April 2022, the Company entered into a long-term supply agreement with General Motors Company (NYSE: GM) (“GM”) to supply U.S.-sourced and manufactured rare earth materials, alloy and finished magnets for the electric motors in more than a dozen models using GM’s Ultium Platform, with a gradual production ramp that is expected to begin in late 2023. These developments are part of the Company’s Stage III downstream expansion strategy (“Stage III”). 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 (“CODM”), or decision-making group, in deciding how to allocate resources and in assessing performance. The Company’s CODM 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 robotics, 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, since they are interim statements, 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 Form 10-K.

SIGNIFICANT ACCOUNTING POLICIES

SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2023
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. 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. Concentration of Risk: Financial instruments that potentially subject the Company to credit risk consist principally of cash, cash equivalents and short-term investments, and trade accounts receivable. The Company believes that its credit risk is limited because the Company’s current contracts are with companies that have a reliable payment history. The Company does not believe that it is exposed to any significant risks related to its cash accounts, money market funds, or short-term investments. As of September 30, 2023, Shenghe was the Company’s principal customer and accounted for more than 90% of revenue. Rare earth concentrate is not quoted on any major commodities market or exchange and demand for rare earth concentrate is currently constrained to a relatively limited number of refiners, a significant majority of which are based in China. Uncertainty exists as to the market price of rare earth oxide (“REO”), as evidenced by the volatility experienced in 2022 and continued into 2023 due to concerns over the global economic conditions and actual or perceived concerns over increases in the supply of rare earth products. Furthermore, while revenue is generated in the U.S., Shenghe conducts its primary operations in China and may transport and sell products in the Chinese market. Note 15 , “Related-Party Transactions,” for additional information. At the onset of the COVID-19 pandemic and through 2022, the Company experienced, at times, significant shipping delays due to congestion and slowdowns at U.S. and international ports caused by shortages in vessels, containers, and truckers, also disrupting the global supply chain. Despite these factors, the Company did not experience a reduction in production or sales due to the COVID-19 pandemic. However, the COVID-19 pandemic contributed to certain cost and schedule pressures for capital projects. The Company continues to monitor the global situation, including the impacts of new and potential future variants of COVID-19, or other factors that may affect international shipping, logistics, and supply chain, or involve responses to government actions such as strikes or other disruptions. Intangible Assets: Indefinite-lived intangible assets are tested annually for impairment, or more frequently if events or changes in circumstances indicate that it is more likely than not that the assets are impaired. If the carrying amounts of the indefinite-lived intangible assets exceed their fair value, the excess amount is recognized as an impairment. Intangible assets that have a definite life are amortized on a straight-line basis over their estimated useful lives to reflect the expected pattern of economic benefits consumed. The Company reviews the carrying amount of its amortizing intangible assets for possible impairment whenever events or changes in circumstances indicate that their carrying amount may not be recoverable. If the carrying amounts of the amortizing intangible assets exceed their fair value, the excess amount is recognized as an impairment. Once an impairment of an intangible asset has been recorded, it cannot be reversed. No impairment charges were recorded during the three and nine months ended September 30, 2023 and 2022. See also Note 6 , “ Intangible Assets.” Leases: The Company determines if an arrangement is, or contains, a lease at contract inception. In some cases, the Company has determined that its lease arrangements include both lease and non-lease components. The Company has elected to use a practical expedient to account for each separate lease component and its associated non-lease components as a single lease component for the majority of its asset classes. The Company recognizes right-of-use (“ROU”) assets and lease liabilities upon commencement for all leases with a lease term greater than 12 months. The Company has elected to use a practical expedient to not recognize leases with a lease term of 12 months or less in the unaudited Condensed Consolidated Balance Sheets for the majority of its asset classes. These short-term leases are expensed on a straight-line basis over the lease term. ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at commencement date of the lease based on the present value of lease payments over the lease term. When the rate implicit in the lease cannot be readily determined, the Company utilizes its incremental borrowing rate in determining the present value of the future lease payments. Lease liabilities are accreted each period and reduced for payments. The ROU asset also includes other adjustments, such as for the effects of lease prepayments, initial lease costs, or lease incentives received. The lease term may include periods covered by options to extend or terminate the lease when it is either reasonably certain that the Company will exercise a renewal option, or reasonably certain it will not exercise an early termination option. For operating leases, lease expense is recognized on a straight-line basis over the lease term. For finance leases, the ROU asset amortizes on a straight-line basis over the shorter of the lease term or the useful life of the underlying asset (or the useful life of the underlying asset if title transfers at the end of the lease term or there is a purchase option the Company is reasonably certain to exercise) and the lease liability accretes interest based on the interest method using the discount rate determined at lease commencement. For operating and finance leases, variable lease payments not included in the lease liability are expensed as incurred unless such costs are capitalized as part of another asset (e.g., inventory). Additionally, ROU assets are subject to impairment testing whenever events or changes in circumstances indicate that their carrying amount may not be recoverable. If the carrying amounts of ROU assets exceed their fair value, the excess amount is recognized as an impairment. No impairment charges were recorded during the three and nine months ended September 30, 2023 and 2022. See also Note 9 , “Leases.” Stock-Based Compensation: The cost of employee services received in exchange for an award of equity instruments is based on the grant-date fair value of the award. The fair value of Stock Awards (as defined in Note 12 , “Stock-based Compensation,” ) is equal to the fair value of the Company’s stock on the grant date. The fair value of performance awards that include performance and/or market conditions is determined using a Monte Carlo simulation technique. The Monte Carlo simulation requires the use of inputs and assumptions such as the grant-date closing stock price, expected volatility, correlation coefficient to relevant peer groups or indices, risk-free interest rate and dividend yield. Compensation cost for Stock Awards with graded vesting schedules is recognized on a straight-line basis over the requisite service period for each separately vesting portion of the award as if the award was, in substance, multiple awards, which results in accelerated recognition of compensation cost. Compensation cost for performance awards with cliff vesting schedules is recognized on a straight-line basis over the requisite service period. Compensation cost is not adjusted based on the actual achievement of the market-based performance goals. The Company accounts for forfeitures in the period in which they occur based on actual forfeitures. See also Note 12 , “Stock-based Compensation.” Recently Issued Accounting Pronouncements: During the three and nine months ended September 30, 2023, there were no accounting pronouncements adopted by the Company that had a material impact on the Company’s unaudited Condensed Consolidated Financial Statements. Additionally, as of September 30, 2023, there were no accounting pronouncements pending adoption that are expected to have a material impact on the Company's unaudited Condensed Consolidated Financial Statements. Reclassifications: Certain amounts in prior periods have been reclassified to conform to the current year presentation.

CASH, CASH EQUIVALENTS AND INVE

CASH, CASH EQUIVALENTS AND INVESTMENTS	9 Months Ended
	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
CASH, CASH EQUIVALENTS AND INVESTMENTS	CASH, CASH EQUIVALENTS AND INVESTMENTS The following table presents the Company’s cash, cash equivalents and short-term investments: September 30, 2023 December 31, 2022 (in thousands) Amortized Cost Basis Unrealized Gains Unrealized Losses Estimated Fair Value Amortized Cost Basis Unrealized Gains Unrealized Losses Estimated Fair Value Cash: Demand deposits $ 1,580 $ — $ — $ 1,580 $ 7,373 $ — $ — $ 7,373 Cash equivalents: Money market funds 134,038 — — 134,038 64,855 — — 64,855 U.S. agency securities — — — — 63,605 1 (2) 63,604 U.S. Treasury securities 327,224 48 (4) 327,268 795 — — 795 Commercial paper 49,662 7 — 49,669 — — — — Certificates of deposit 35,110 3 — 35,113 — — — — Total cash equivalents 546,034 58 (4) 546,088 129,255 1 (2) 129,254 Total cash and equivalents 547,614 58 (4) 547,668 136,628 1 (2) 136,627 Short-term investments: U.S. agency securities 141,873 1 (155) 141,719 979,878 361 (17) 980,222 U.S. Treasury securities 395,217 61 (3) 395,275 65,586 1 (91) 65,496 Total short-term investments 537,090 62 (158) 536,994 1,045,464 362 (108) 1,045,718 Total cash, cash equivalents and short-term investments $ 1,084,704 $ 120 $ (162) $ 1,084,662 $ 1,182,092 $ 363 $ (110) $ 1,182,345 The Company does not intend to sell, nor is it more likely than not that the Company will be required to sell, any investments in unrealized loss positions before recovery of their amortized cost basis. The Company did not recognize any credit losses related to its available-for-sale investments during the three and nine months ended September 30, 2023 and 2022. The unrealized losses on the Company’s available-for-sale investments were primarily due to unfavorable changes in interest rates subsequent to initial purchase. None of the available-for-sale investments held as of September 30, 2023, were in a continuous unrealized loss position for greater than 12 months and the unrealized losses and the related risk of expected credit losses were not material. The Company recognized the following income and expense amounts, all of which are included in “Other income, net” within the Company’s unaudited Condensed Consolidated Statements of Operations: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Gross realized gains $ 1 $ 71 $ 506 $ 71 Gross realized losses $ — $ 199 $ 139 $ 199 Interest and investment income (1) $ 14,455 $ 6,274 $ 41,607 $ 8,529 (1) Includes interest and investment income on the Company’s available-for-sale securities and other money market funds. As of September 30, 2023, the fair values of available-for-sale investments, by remaining contractual maturity, were as follows: (in thousands) Due within one year $ 926,223 Due after one year through two years 22,821 Total $ 949,044

INVENTORIES

INVENTORIES	9 Months Ended
	Sep. 30, 2023
Inventory Disclosure [Abstract]
INVENTORIES	INVENTORIES The Company’s inventories consisted of the following: September 30, 2023 December 31, 2022 (in thousands) Raw materials and supplies, including spare parts (1) $ 34,680 $ 28,590 Work in process (2) 41,367 27,212 Finished goods 1,132 1,752 Total current inventories 77,179 57,554 Add: Non-current portion (3) 12,589 5,744 Total inventories $ 89,768 $ 63,298 (1) Includes raw materials to support activities pertaining to the Company’s rare earth metal, alloy and magnet manufacturing capabilities. (2) Includes packaged and finished NdPr oxide shipped to the Company’s toller for processing into NdPr metal. (3) Represents stockpiled ore that is not expected to be processed within the next 12 months as well as certain raw materials that are not expected to be consumed within the next 12 months.

PROPERTY, PLANT AND EQUIPMENT

PROPERTY, PLANT AND EQUIPMENT	9 Months Ended
	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT	PROPERTY, PLANT AND EQUIPMENT The Company’s property, plant and equipment consisted of the following: September 30, 2023 December 31, 2022 (in thousands) Land and land improvements $ 16,425 $ 16,102 Buildings and building improvements 25,427 15,111 Machinery and equipment 473,578 186,388 Assets under construction 240,219 338,482 Mineral rights 438,395 438,395 Property, plant and equipment, gross 1,194,044 994,478 Less: Accumulated depreciation and depletion (96,317) (58,735) Property, plant and equipment, net $ 1,097,727 $ 935,743 Additions to Property, Plant and Equipment: The Company capitalized expenditures related to property, plant and equipment of $199.9 million and $250.1 million for the nine months ended September 30, 2023 and 2022, respectively, including amounts not yet paid (see Note 16 , “Supplemental Cash Flow Information” ). The capitalized expenditures related to machinery, equipment, and assets under construction to support the Company’s Stage II optimization project, its Fort Worth Facility, and its HREE Facility (as defined below). Additionally, t he capitalized expenditures for the nine months ended September 30, 2022, included the purchase of approximately 18 acres of land in Fort Worth, Texas . Placement of Certain Stage II Assets into Service: During the nine months ended September 30, 2023 , the Company transferred certain of its assets totaling $248.4 million and pertaining to its Stage II optimization project from assets under construction to buildings, machinery and equipment, with $239.8 million relating to machinery and equipment. Government Awards: In November 2020, the Company was awarded a Defense Production Act Title III technology investment agreement (“TIA”) from the Department of Defense (“DOD”) to establish domestic processing for separated light rare earth elements in the amount of $9.6 million. During the nine months ended September 30, 2023 and 2022, pursuant to the TIA, the Company had received zero and $5.1 million, respectively, in reimbursements from the DOD. As of September 30, 2023, the Company is entitled to receive an additional $0.1 million from the DOD under the TIA. In February 2022, the Company was awarded a $35.0 million contract by the DOD’s Office of Industrial Base Analysis and Sustainment program to design and build a facility to process heavy rare earth elements (“HREE”) at Mountain Pass (the “HREE Facility”) (the “HREE Production Project Agreement”). As of September 30, 2023, the Company had received $1.1 million from the DOD under the HREE Production Project Agreement. Change in Estimates of Asset Retirement Costs: As a result of a decrement to the Company’s asset retirement obligations during the third quarter of 2022, the carrying amount of the Company’s total property, plant and equipment was reduced by $10.4 million, the majority of which pertained to buildings, machinery and equipment, and assets under construction, in the amounts of $0.6 million, $2.7 million and $6.7 million, respectively. Additionally, the Company’s depreciation expense for the three and nine months ended September 30, 2022, was reduced by $2.7 million, reflecting the excess of the decrement over the carrying amount of the related property, plant and equipment. See Note 7 , “Asset Retirement and Environmental Obligations,” for further information on the decrement. The Company’s depreciation and depletion expense were as follows: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Depreciation expense (1) $ 13,951 $ (656) $ 28,385 $ 3,702 Depletion expense $ 2,664 $ 2,664 $ 8,407 $ 8,808 (1) As noted above, during the three months ended September 30, 2022, the Company recorded a reduction to depreciation expense, reflecting the excess of the asset retirement obligation decrement over the carrying amount of the related property, plant and equipment, as a result of changes in the Company’s estimates of cash flows underlying its asset retirement obligations. The Company recognized $0.8 million and $5.5 million of demolition costs for the three and nine months ended September 30, 2023, which are included in “Loss on disposals of long-lived assets, net” within the Company’s unaudited Condensed Consolidated Statements of Operations, incurred in connection with demolishing and removing certain old facilities from the Mountain Pass site that have not been used in the Company’s operations. There were no impairments recognized for the three and nine months ended September 30, 2023 and 2022.

INTANGIBLE ASSETS

INTANGIBLE ASSETS	9 Months Ended
	Sep. 30, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
INTANGIBLE ASSETS	INTANGIBLE ASSETS In August 2023, the Company acquired a license to use patented technology, technical know-how, and other intellectual property pertaining to the development and manufacturing of magnetics products in exchange for 435,729 shares of the Company’s common stock. Pursuant to the terms of the agreement to acquire the license, 152,504 shares were issued immediately and the remaining shares will be issued as follows: 43,573 on each of the first, second, and third anniversaries of the acquisition date and an additional 152,506 shares on the fourth anniversary of the acquisition date. Upon obtaining the license, the Company recorded a definite-lived intangible asset in the amount of $9.0 million, based on the closing price of the Company’s common stock on the acquisition date. The intangible asset will be amortized on a straight-line basis, with no estimated residual value, over the estimated useful life of 7.5 years, which the Company based on the life of the patents associated with the licensed technology. Contemporaneous with the acquisition of the license, the Company entered into a consulting agreement in support of integrating the licensed technology and know-how into its existing processes aimed at the development of magnetics products. Unless earlier terminated, under the consulting agreement, the Company will pay a total of approximately $15 million over the next four years, of which, the first payment will be in cash on the first anniversary of the consulting agreement and the payments pertaining to the second, third, and fourth anniversaries of the consulting agreement may be settled in cash or shares of the Company’s common stock at the Company’s election. The Company will ratably record an expense over the four-year period unless the costs qualify for capitalization. The Company’s intangible assets were as follows: September 30, 2023 December 31, 2022 (in thousands) Intangible assets with indefinite lives: Emissions allowances $ 316 $ 89 Intangible assets with definite lives: Patent and intellectual property license 8,963 — Less: Accumulated amortization (100) — Patent and intellectual property license, net 8,863 — Intangible assets, net $ 9,179 $ 89 Amortization expense related to amortizing intangible assets was $0.1 million for the three and nine months ended September 30, 2023. There was no amortization expense related to amortizing intangible assets recognized for the three and nine months ended September 30, 2022. The following table presents the estimated amortization expense based on amortizing intangible assets as of September 30, 2023: (in thousands) Period: Remainder of 2023 $ 299 2024 1,195 2025 1,195 2026 1,195 2027 1,195 Thereafter 3,784 Total $ 8,863

ASSET RETIREMENT AND ENVIRONMEN

ASSET RETIREMENT AND ENVIRONMENTAL OBLIGATIONS	9 Months Ended
	Sep. 30, 2023
Asset Retirement Obligation Disclosure [Abstract]
ASSET RETIREMENT AND ENVIRONMENTAL OBLIGATIONS	ASSET RETIREMENT AND ENVIRONMENTAL OBLIGATIONS Asset Retirement Obligations The Company estimates asset retirement obligations based on the requirements to reclaim certain land areas associated with mineral extraction activities and certain related facilities at Mountain Pass. Minor reclamation activities related to discrete portions of the Company’s operations are ongoing. As of September 30, 2023, the Company estimated a significant portion of the cash outflows for major reclamation activities including the retirement of Mountain Pass will be incurred beginning in 2056 and 2057. In June 2021, San Bernardino County approved a re-zoning request for certain of the Company’s properties such that certain of the Company’s processing and separations facilities would be zoned for industrial end uses as opposed to the prior “resource conservation” designation. In September 2022, and as a result of the re-zoning of this land, the Company received final approval from San Bernardino County and the Division of Mine Reclamation (California) on a revised reclamation plan. The revision removed from the regulatory oversight under The Surface Mining and Reclamation Act of 1975 the majority of the buildings and equipment used in the processing and separations facilities, including the land underlying such buildings and equipment. As a result of the final approval of the reclamation plan, in the third quarter of 2022, the Company revised its estimated cash flows pertaining to the settlement of the reclamation and removal activities associated with Mountain Pass, including removing the previous estimates of the cash flows associated with the processing and separations facilities that no longer require reclamation. The changes in estimates resulted in an asset retirement obligation decrement of $13.1 million, of which $10.4 million reduced the carrying amounts of the associated property, plant and equipment, and $2.7 million, reflecting the excess of the decrement over the carrying amount of the related property, plant and equipment, was recorded as a reduction to depreciation expense for the three and nine months ended September 30, 2022. As of September 30, 2023, the credit-adjusted risk-free rate ranged between 6.5% and 12.0% depending on the timing of expected settlement and when the increment was recognized. There were no significant increments or decrements for the three and nine months ended September 30, 2023, and there were no significant increments for the three and nine months ended September 30, 2022. The balance as of both September 30, 2023, and December 31, 2022, included current portions of $0.2 million, which are included in “Other current liabilities” within the Company’s unaudited Condensed Consolidated Balance Sheets. The total estimated future undiscounted cash flows required to satisfy the Company’s asset retirement obligations were $50.3 million and $50.4 million as of September 30, 2023, and December 31, 2022, respectively. Environmental Obligations The Company has 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, the Company developed an estimate of future cash payments for the remediation plan. As of September 30, 2023, the Company estimated the cash outflows related to these environmental activities will be incurred annually over the next 24 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 significant changes in the estimated remaining remediation costs for the three and nine months ended September 30, 2023 and 2022. The total estimated aggregate undiscounted cost of $26.8 million and $27.2 million as of September 30, 2023, and December 31, 2022, respectively, principally related to water monitoring activities required by state and local agencies. Based on the Company’s estimate of the cost and timing and the assumption that payments are considered to be fixed and reliably determinable, the Company has discounted the liability. The balance as of both September 30, 2023, and December 31, 2022, included current portions of $0.5 million, which are included in “Other current liabilities” within the Company’s unaudited Condensed Consolidated Balance Sheets. Financial Assurances The Company is required to provide the applicable government agencies with financial assurances relating to the closure and reclamation obligations. As of September 30, 2023, and December 31, 2022, the Company had financial assurance requirements of $45.4 million and $43.5 million, respectively, which were satisfied with surety bonds placed with California state and regional agencies.

DEBT OBLIGATIONS

DEBT OBLIGATIONS	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
DEBT OBLIGATIONS	DEBT OBLIGATIONS The Company’s long-term debt was as follows: September 30, 2023 December 31, 2022 (in thousands) Convertible Notes due 2026 $ 690,000 $ 690,000 Less: Unamortized debt issuance costs (8,906) (11,556) Long-term debt, net $ 681,094 $ 678,444 Convertible Notes In March 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 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. 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 price exceed 28.5714 shares of common stock per $1,000 principal amount of the Convertible Notes. As of September 30, 2023, based on the conversion price, the maximum number of shares that could be issued to satisfy the conversion feature of the Convertible Notes was 19,714,266. The Convertible Notes’ if-converted value did not exceed its principal amount as of September 30, 2023. Interest expense related to the Convertible Notes was as follows: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Coupon interest $ 431 $ 431 $ 1,293 $ 1,293 Amortization of debt issuance costs 884 881 2,650 2,637 Convertible Notes interest expense $ 1,315 $ 1,312 $ 3,943 $ 3,930 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 2.5 years as of September 30, 2023. Equipment Notes The Company has entered into several financing agreements for the purchase of equipment, including trucks, tractors, loaders, graders, and various other machinery. 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. 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: September 30, 2023 December 31, 2022 (in thousands) Equipment notes Current $ 2,193 $ 2,392 Non-current 3,147 4,743 $ 5,340 $ 7,135 As of September 30, 2023, none of the agreements or indentures governing the Company’s indebtedness contain financial covenants.

LEASES

LEASES	9 Months Ended
	Sep. 30, 2023
Leases [Abstract]
LEASES	LEASES The Company has operating and finance leases for certain office space, warehouses, vehicles and equipment used in its operations. In November 2021, the Company entered into a lease agreement for corporate office space. The lease commenced during the second quarter of 2023, and at lease commencement, the Company recorded an operating lease liability of $7.3 million and an ROU asset of $10.3 million, primarily comprised of the lease liability as well as $2.9 million of payments for lessor-owned tenant improvements. The lease has an initial term of 91 months expiring in October 2030, with an option to renew for one five-year period at the election of the Company. Excluding rent abatement in the first year of the lease, the initial annual base rent payment is $1.2 million, subject to an annual escalator. The Company’s lease agreements do not contain material residual value guarantees or restrictive covenants. As of September 30, 2023, the Company was not reasonably certain of exercising any material purchase, renewal, or termination options contained within its lease agreements. As of September 30, 2023, the maturities of the Company’s operating and finance lease liabilities were as follows: (in thousands) Operating Leases Finance Leases Period: Remainder of 2023 $ 162 $ 56 2024 1,422 228 2025 1,441 179 2026 1,337 59 2027 1,370 54 Thereafter 4,066 160 Total lease payments 9,798 736 Less: Imputed interest (2,056) (108) Total $ 7,742 $ 628 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 September 30, 2023 December 31, 2022 (in thousands) Operating Leases: Right-of-use assets Operating lease right-of-use assets $ 10,346 $ 99 Operating lease liability, current Operating lease liabilities (included in current liabilities) $ 728 $ 84 Operating lease liability, non-current Operating lease liabilities (included in non-current liabilities) 7,014 15 Total operating lease liabilities $ 7,742 $ 99 Finance Leases: Right-of-use assets Other non-current assets $ 650 $ 451 Finance lease liability, current Other current liabilities $ 197 $ 354 Finance lease liability, non-current Other non-current liabilities 431 242 Total finance lease liabilities $ 628 $ 596
LEASES	LEASES The Company has operating and finance leases for certain office space, warehouses, vehicles and equipment used in its operations. In November 2021, the Company entered into a lease agreement for corporate office space. The lease commenced during the second quarter of 2023, and at lease commencement, the Company recorded an operating lease liability of $7.3 million and an ROU asset of $10.3 million, primarily comprised of the lease liability as well as $2.9 million of payments for lessor-owned tenant improvements. The lease has an initial term of 91 months expiring in October 2030, with an option to renew for one five-year period at the election of the Company. Excluding rent abatement in the first year of the lease, the initial annual base rent payment is $1.2 million, subject to an annual escalator. The Company’s lease agreements do not contain material residual value guarantees or restrictive covenants. As of September 30, 2023, the Company was not reasonably certain of exercising any material purchase, renewal, or termination options contained within its lease agreements. As of September 30, 2023, the maturities of the Company’s operating and finance lease liabilities were as follows: (in thousands) Operating Leases Finance Leases Period: Remainder of 2023 $ 162 $ 56 2024 1,422 228 2025 1,441 179 2026 1,337 59 2027 1,370 54 Thereafter 4,066 160 Total lease payments 9,798 736 Less: Imputed interest (2,056) (108) Total $ 7,742 $ 628 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 September 30, 2023 December 31, 2022 (in thousands) Operating Leases: Right-of-use assets Operating lease right-of-use assets $ 10,346 $ 99 Operating lease liability, current Operating lease liabilities (included in current liabilities) $ 728 $ 84 Operating lease liability, non-current Operating lease liabilities (included in non-current liabilities) 7,014 15 Total operating lease liabilities $ 7,742 $ 99 Finance Leases: Right-of-use assets Other non-current assets $ 650 $ 451 Finance lease liability, current Other current liabilities $ 197 $ 354 Finance lease liability, non-current Other non-current liabilities 431 242 Total finance lease liabilities $ 628 $ 596

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2023
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The 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 or deficiencies 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 tax expense or benefit as a percentage of income or loss before income taxes) including discrete items was 4.5% and 24.5% for the three and nine months ended September 30, 2023, respectively, as compared to 24.9% and 24.5% for the three and nine months ended September 30, 2022, respectively. The Company’s effective income tax rate can vary from period to period depending on, among other factors, percentage depletion, executive compensation deduction limitations, the Section 45X Advanced Manufacturing Production Credit, and changes to its valuation allowance against deferred tax assets. Certain of these and other factors, including the Company’s history and projections of pretax earnings, are considered in assessing its ability to realize its net deferred tax assets. On August 16, 2022, the U.S. government enacted the Inflation Reduction Act of 2022 which, among other things, implements a 15% minimum tax on book income of certain large corporations, a 1% excise tax on net stock repurchases, and provides several tax incentives to promote clean energy for tax years beginning after December 31, 2022. The Company does not expect the minimum tax or excise tax to have a material impact on the unaudited Condensed Consolidated Financial

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Litigation: The Company may become party to lawsuits, administrative proceedings, and government investigations, including environmental, regulatory, construction, and other matters, in the ordinary course of business. Large, and sometimes unspecified, damages or penalties may be sought in some matters, and certain matters may require years to resolve. The Company is not aware of any pending or threatened litigation that it believes would have a material adverse effect on its unaudited Condensed Consolidated Financial Statements.

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	9 Months Ended
	Sep. 30, 2023
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 (“SARs”); restricted stock, restricted stock units (“RSUs”) and other stock awards (collectively, the “Stock Awards”); and performance awards, which vest contingent upon the attainment of either or a combination of market- or performance-based goals. As of September 30, 2023, the Company has not issued any stock options or SARs and there were 6,101,859 shares available for future grants under the 2020 Incentive Plan. Market-Based PSUs: In February 2023, pursuant to the 2020 Incentive Plan, the Company’s Compensation Committee of the Board of Directors adopted a performance share plan (the “2023 Performance Share Plan”). Pursuant to the 2023 Performance Share Plan, for the nine months ended September 30, 2023, the Company granted 62,709 of market-based performance stock units (“PSUs”) at target, all of which cliff vest after a requisite performance and service period of three years. The PSUs have the potential to be earned at between 0% and 200% of the number of awards granted depending on the level of growth of the Company’s total shareholder return (“TSR”) as compared to the TSR of the S&P 400 Index and the S&P 400 Materials Group over the performance period. The fair value of the market-based PSUs was determined using a Monte Carlo simulation technique. Stock-Based Compensation: The Company’s stock-based compensation was recorded as follows: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Cost of sales $ 842 $ 889 $ 2,759 $ 2,110 Selling, general and administrative 5,193 6,912 15,603 22,717 Advanced projects, start-up, development and other 263 5 679 192 Total stock-based compensation expense $ 6,298 $ 7,806 $ 19,041 $ 25,019 Stock-based compensation capitalized to property, plant and equipment, net $ 367 $ 267 $ 1,566 $ 951

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTSAccounting Standards Codification (“ASC”) Topic 820, “Fair Value Measurement” (“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. Short-term Investments The fair value of the Company’s short-term investments, which are classified as available-for-sale securities, is estimated based on quoted prices in active markets and is classified as a Level 1 measurement. 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. 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. 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: September 30, 2023 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 547,668 $ 547,668 $ 547,668 $ — $ — Short-term investments $ 536,994 $ 536,994 $ 536,994 $ — $ — Restricted cash $ 1,575 $ 1,575 $ 1,575 $ — $ — Financial liabilities: Convertible Notes $ 681,094 $ 591,923 $ 591,923 $ — $ — Equipment notes $ 5,340 $ 5,142 $ — $ 5,142 $ — December 31, 2022 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 136,627 $ 136,627 $ 136,627 $ — $ — Short-term investments $ 1,045,718 $ 1,045,718 $ 1,045,718 $ — $ — Restricted cash $ 6,882 $ 6,882 $ 6,882 $ — $ — Financial liabilities: Convertible Notes $ 678,444 $ 610,650 $ 610,650 $ — $ — Equipment notes $ 7,135 $ 6,807 $ — $ 6,807 $ —

EARNINGS (LOSS) PER SHARE

EARNINGS (LOSS) PER SHARE	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
EARNINGS (LOSS) PER SHARE	EARNINGS (LOSS) PER SHARE Basic earnings (loss) per share is computed by dividing net income (loss) by the weighted-average number of common shares outstanding during the period. Diluted earnings (loss) per share is computed by dividing net income (loss) 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 earnings (loss) per share to the weighted-average common shares outstanding used in the calculation of diluted earnings (loss) per share: For the three months ended September 30, For the nine months ended September 30, 2023 2022 2023 2022 Weighted-average shares outstanding, basic 177,231,717 176,543,624 177,034,068 176,476,276 Assumed conversion of Convertible Notes — 15,584,409 15,584,409 15,584,409 Assumed conversion of restricted stock — 840,786 620,190 944,925 Assumed conversion of RSUs — 441,038 393,995 433,329 Weighted-average shares outstanding, diluted 177,231,717 193,409,857 193,632,662 193,438,939 The following table presents unweighted potentially dilutive shares that were not included in the computation of diluted earnings (loss) per share because to do so would have been antidilutive: For the three months ended September 30, For the nine months ended September 30, 2023 2022 2023 2022 Convertible Notes 15,584,409 — — — Restricted Stock 685,202 — — — RSUs 1,629,938 6,013 3,184 6,013 The following table presents the calculation of basic and diluted earnings (loss) per share for the Company’s common stock: For the three months ended September 30, For the nine months ended September 30, (in thousands, except share and per share data) 2023 2022 2023 2022 Calculation of basic earnings (loss) per share: Net income (loss) $ (4,276) $ 63,177 $ 40,566 $ 221,997 Weighted-average shares outstanding, basic 177,231,717 176,543,624 177,034,068 176,476,276 Basic earnings (loss) per share $ (0.02) $ 0.36 $ 0.23 $ 1.26 Calculation of diluted earnings (loss) per share: Net income (loss) $ (4,276) $ 63,177 $ 40,566 $ 221,997 Interest expense, net of tax (1) : Convertible Notes — 985 2,977 2,967 Diluted income (loss) $ (4,276) $ 64,162 $ 43,543 $ 224,964 Weighted-average shares outstanding, diluted 177,231,717 193,409,857 193,632,662 193,438,939 Diluted earnings (loss) per share $ (0.02) $ 0.33 $ 0.22 $ 1.16 (1) The nine months ended September 30, 2023, was tax-effected at a rate of 24.5%, and the three and nine months ended September 30, 2022, were tax-effected at a rate of 24.9% and 24.5%, respectively.

RELATED PARTY TRANSACTIONS

RELATED PARTY TRANSACTIONS	9 Months Ended
	Sep. 30, 2023
Related Party Transactions [Abstract]
RELATED PARTY TRANSACTIONS	RELATED-PARTY TRANSACTIONS Offtake Agreement: In March 2022, the Company entered into an offtake agreement (the “Offtake Agreement”) 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. The Offtake Agreement became effective upon the termination of the amended and restated offtake agreement with Shenghe. The initial term of the Offtake Agreement is two years, with the option to extend the term at the Company’s discretion for an additional one-year period. Pursuant to the Offtake Agreement, and subject to certain exclusions, Shenghe is obligated to purchase on a “take or pay” basis the rare earth concentrate produced by the Company as the exclusive distributor in China, with certain exceptions for the Company’s direct sales globally. In addition, at the discretion of the Company, Shenghe may be required to purchase on a “take or pay” basis certain non-concentrate rare earth products, although the Company may sell all non-concentrate rare earth products in its sole discretion to customers or end users in any jurisdiction. The sales price of rare earth concentrate sold to Shenghe is based on an agreed-upon price per metric ton, subject to certain quality adjustments depending on the measured characteristics of the product, with an adjustment for the ultimate market price of the product realized by Shenghe upon sales to their customers. The sales price and other terms applicable to a quantity of offtake products are set forth in monthly purchase agreements between the Company and Shenghe. Under the Offtake Agreement, Shenghe is paid a variable commission on net proceeds to the Company. Tolling Agreement with VREX Holdco: In October 2023, the Company entered into a tolling agreement with VREX Holdco Ltd. Pte. (“VREX Holdco”) (the “Tolling Agreement”), a wholly-owned subsidiary of Shenghe. VREX Holdco owns Vietnam Rare Earth Company Limited (“VREX”), which owns and operates a metal processing plant and related facilities in Vietnam. This Tolling Agreement replaced the previous tolling agreement signed in March 2023 directly with VREX. Pursuant to the Tolling Agreement, the Company will deliver NdPr oxide to VREX Holdco, which VREX Holdco will then provide to VREX to process into NdPr metal for delivery to the Company’s customers globally. As several of the Company’s potential customers that manufacture magnets outside of China prefer to purchase NdPr metal in addition to NdPr oxide, this Tolling Agreement will enable the Company to distribute NdPr products more widely to customers in Japan and other global markets. During the term of the Tolling Agreement, the Company will pay VREX Holdco a processing fee per unit of rare earth metal produced. The Company will maintain title to the products and directly enter into sales agreements for the produced NdPr metal. The initial term of the Tolling Agreement is three years and may be renewed for additional three-year terms. As of September 30, 2023, there have not been any transactions as contemplated under the previous tolling agreement signed in March 2023. Revenue and Cost of Sales: The Company’s related-party revenue and cost of sales were as follows: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Revenue: Rare earth concentrate $ 51,502 $ 114,894 $ 203,186 $ 401,496 Other rare earth products (1) $ — $ 172 $ — $ 8,646 Cost of sales (2) $ 21,829 $ 21,842 $ 66,817 $ 65,368 (1) Represents sales agreements with Shenghe for non-concentrate products, including certain stockpiles of rare earth fluoride. (2) Excludes depreciation, depletion and amortization and includes shipping and freight. Purchases of Materials and Supplies: The Company purchases certain reagent products (generally produced by an unrelated third-party manufacturer) used in the flotation process as well as other materials from Shenghe in the ordinary course of business. Total purchases were $5.8 million and $7.6 million for the three and nine months ended September 30, 2023, respectively, as compared to $15.3 million and $18.5 million for the three and nine months ended September 30, 2022, respectively. Accounts Receivable: As of September 30, 2023, and December 31, 2022, $11.9 million and $29.8 million, respectively, of the accounts receivable as stated in the unaudited Condensed Consolidated Balance Sheets, were receivable from and pertained to sales made to Shenghe in the ordinary course of business.

SUPPLEMENTAL CASH FLOW INFORMAT

SUPPLEMENTAL CASH FLOW INFORMATION	9 Months Ended
	Sep. 30, 2023
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 nine months ended September 30, (in thousands) 2023 2022 Supplemental cash flow information: Cash paid for interest $ 1,116 $ 1,140 Cash payments related to income taxes $ 23,101 $ 16,827 Change in construction payables $ 10,952 $ 35,779 Supplemental non-cash investing and financing activities: Common stock issued to acquire intangible asset $ 8,963 $ — Operating ROU assets obtained in exchange for lease liabilities $ 7,608 $ 168 Revenue recognized in exchange for debt principal reduction $ — $ 13,566 Decrease in estimates of asset retirement costs $ — $ 10,395

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net income	$ (4,276)	$ 63,177	$ 40,566	$ 221,997

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

SIGNIFICANT ACCOUNTING POLICI_2

SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2023
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, since they are interim statements, 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 Form 10-K.
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.
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.
Concentration of Risk	Financial instruments that potentially subject the Company to credit risk consist principally of cash, cash equivalents and short-term investments, and trade accounts receivable. The Company believes that its credit risk is limited because the Company’s current contracts are with companies that have a reliable payment history. The Company does not believe that it is exposed to any significant risks related to its cash accounts, money market funds, or short-term investments. As of September 30, 2023, Shenghe was the Company’s principal customer and accounted for more than 90% of revenue. Rare earth concentrate is not quoted on any major commodities market or exchange and demand for rare earth concentrate is currently constrained to a relatively limited number of refiners, a significant majority of which are based in China. Uncertainty exists as to the market price of rare earth oxide (“REO”), as evidenced by the volatility experienced in 2022 and continued into 2023 due to concerns over the global economic conditions and actual or perceived concerns over increases in the supply of rare earth products. Furthermore, while revenue is generated in the U.S., Shenghe conducts its primary operations in China and may transport and sell products in the Chinese market. Note 15 , “Related-Party Transactions,” for additional information. At the onset of the COVID-19 pandemic and through 2022, the Company experienced, at times, significant shipping delays due to congestion and slowdowns at U.S. and international ports caused by shortages in vessels, containers, and truckers, also disrupting the global supply chain. Despite these factors, the Company did not experience a reduction in production or sales due to the COVID-19 pandemic. However, the COVID-19 pandemic contributed to certain cost and schedule pressures for capital projects. The Company continues to monitor the global situation, including the impacts of new and potential future variants of COVID-19, or other factors that may affect international shipping, logistics, and supply chain, or involve responses to government actions such as strikes or other disruptions.
Intangible Assets	Indefinite-lived intangible assets are tested annually for impairment, or more frequently if events or changes in circumstances indicate that it is more likely than not that the assets are impaired. If the carrying amounts of the indefinite-lived intangible assets exceed their fair value, the excess amount is recognized as an impairment. Intangible assets that have a definite life are amortized on a straight-line basis over their estimated useful lives to reflect the expected pattern of economic benefits consumed. The Company reviews the carrying amount of its amortizing intangible assets for possible impairment whenever events or changes in circumstances indicate that their carrying amount may not be recoverable. If the carrying amounts of the amortizing intangible assets exceed their fair value, the excess amount is recognized as an impairment. Once an impairment of an intangible asset has been recorded, it cannot be reversed. No impairment charges were recorded during the three and nine months ended September 30, 2023 and 2022.
Leases	The Company determines if an arrangement is, or contains, a lease at contract inception. In some cases, the Company has determined that its lease arrangements include both lease and non-lease components. The Company has elected to use a practical expedient to account for each separate lease component and its associated non-lease components as a single lease component for the majority of its asset classes. The Company recognizes right-of-use (“ROU”) assets and lease liabilities upon commencement for all leases with a lease term greater than 12 months. The Company has elected to use a practical expedient to not recognize leases with a lease term of 12 months or less in the unaudited Condensed Consolidated Balance Sheets for the majority of its asset classes. These short-term leases are expensed on a straight-line basis over the lease term.ROU assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at commencement date of the lease based on the present value of lease payments over the lease term. When the rate implicit in the lease cannot be readily determined, the Company utilizes its incremental borrowing rate in determining the present value of the future lease payments. Lease liabilities are accreted each period and reduced for payments. The ROU asset also includes other adjustments, such as for the effects of lease prepayments, initial lease costs, or lease incentives received. The lease term may include periods covered by options to extend or terminate the lease when it is either reasonably certain that the Company will exercise a renewal option, or reasonably certain it will not exercise an early termination option. For operating leases, lease expense is recognized on a straight-line basis over the lease term. For finance leases, the ROU asset amortizes on a straight-line basis over the shorter of the lease term or the useful life of the underlying asset (or the useful life of the underlying asset if title transfers at the end of the lease term or there is a purchase option the Company is reasonably certain to exercise) and the lease liability accretes interest based on the interest method using the discount rate determined at lease commencement. For operating and finance leases, variable lease payments not included in the lease liability are expensed as incurred unless such costs are capitalized as part of another asset (e.g., inventory). Additionally, ROU assets are subject to impairment testing whenever events or changes in circumstances indicate that their carrying amount may not be recoverable. If the carrying amounts of ROU assets exceed their fair value, the excess amount is recognized as an impairment. No impairment charges were recorded during the three and nine months ended September 30, 2023 and 2022.
Stock-Based Compensation	The cost of employee services received in exchange for an award of equity instruments is based on the grant-date fair value of the award. The fair value of Stock Awards (as defined in Note 12 , “Stock-based Compensation,” ) is equal to the fair value of the Company’s stock on the grant date. The fair value of performance awards that include performance and/or market conditions is determined using a Monte Carlo simulation technique. The Monte Carlo simulation requires the use of inputs and assumptions such as the grant-date closing stock price, expected volatility, correlation coefficient to relevant peer groups or indices, risk-free interest rate and dividend yield.
Recently Issued Accounting Pronouncements	During the three and nine months ended September 30, 2023, there were no accounting pronouncements adopted by the Company that had a material impact on the Company’s unaudited Condensed Consolidated Financial Statements. Additionally, as of September 30, 2023, there were no accounting pronouncements pending adoption that are expected to have a material impact on the Company's unaudited Condensed Consolidated Financial Statements.
Reclassifications	Certain amounts in prior periods have been reclassified to conform to the current year presentation.

CASH, CASH EQUIVALENTS AND IN_2

CASH, CASH EQUIVALENTS AND INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract]
Schedule of Debt Securities, Available-for-Sale	The following table presents the Company’s cash, cash equivalents and short-term investments: September 30, 2023 December 31, 2022 (in thousands) Amortized Cost Basis Unrealized Gains Unrealized Losses Estimated Fair Value Amortized Cost Basis Unrealized Gains Unrealized Losses Estimated Fair Value Cash: Demand deposits $ 1,580 $ — $ — $ 1,580 $ 7,373 $ — $ — $ 7,373 Cash equivalents: Money market funds 134,038 — — 134,038 64,855 — — 64,855 U.S. agency securities — — — — 63,605 1 (2) 63,604 U.S. Treasury securities 327,224 48 (4) 327,268 795 — — 795 Commercial paper 49,662 7 — 49,669 — — — — Certificates of deposit 35,110 3 — 35,113 — — — — Total cash equivalents 546,034 58 (4) 546,088 129,255 1 (2) 129,254 Total cash and equivalents 547,614 58 (4) 547,668 136,628 1 (2) 136,627 Short-term investments: U.S. agency securities 141,873 1 (155) 141,719 979,878 361 (17) 980,222 U.S. Treasury securities 395,217 61 (3) 395,275 65,586 1 (91) 65,496 Total short-term investments 537,090 62 (158) 536,994 1,045,464 362 (108) 1,045,718 Total cash, cash equivalents and short-term investments $ 1,084,704 $ 120 $ (162) $ 1,084,662 $ 1,182,092 $ 363 $ (110) $ 1,182,345 The Company recognized the following income and expense amounts, all of which are included in “Other income, net” within the Company’s unaudited Condensed Consolidated Statements of Operations: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Gross realized gains $ 1 $ 71 $ 506 $ 71 Gross realized losses $ — $ 199 $ 139 $ 199 Interest and investment income (1) $ 14,455 $ 6,274 $ 41,607 $ 8,529 (1) Includes interest and investment income on the Company’s available-for-sale securities and other money market funds.
Schedule of Cash and Cash Equivalents	The following table presents the Company’s cash, cash equivalents and short-term investments: September 30, 2023 December 31, 2022 (in thousands) Amortized Cost Basis Unrealized Gains Unrealized Losses Estimated Fair Value Amortized Cost Basis Unrealized Gains Unrealized Losses Estimated Fair Value Cash: Demand deposits $ 1,580 $ — $ — $ 1,580 $ 7,373 $ — $ — $ 7,373 Cash equivalents: Money market funds 134,038 — — 134,038 64,855 — — 64,855 U.S. agency securities — — — — 63,605 1 (2) 63,604 U.S. Treasury securities 327,224 48 (4) 327,268 795 — — 795 Commercial paper 49,662 7 — 49,669 — — — — Certificates of deposit 35,110 3 — 35,113 — — — — Total cash equivalents 546,034 58 (4) 546,088 129,255 1 (2) 129,254 Total cash and equivalents 547,614 58 (4) 547,668 136,628 1 (2) 136,627 Short-term investments: U.S. agency securities 141,873 1 (155) 141,719 979,878 361 (17) 980,222 U.S. Treasury securities 395,217 61 (3) 395,275 65,586 1 (91) 65,496 Total short-term investments 537,090 62 (158) 536,994 1,045,464 362 (108) 1,045,718 Total cash, cash equivalents and short-term investments $ 1,084,704 $ 120 $ (162) $ 1,084,662 $ 1,182,092 $ 363 $ (110) $ 1,182,345
Schedule of Investments Classified by Contractual Maturity Date	As of September 30, 2023, the fair values of available-for-sale investments, by remaining contractual maturity, were as follows: (in thousands) Due within one year $ 926,223 Due after one year through two years 22,821 Total $ 949,044

INVENTORIES (Tables)

INVENTORIES (Tables)	9 Months Ended
	Sep. 30, 2023
Inventory Disclosure [Abstract]
Schedule of Inventories	The Company’s inventories consisted of the following: September 30, 2023 December 31, 2022 (in thousands) Raw materials and supplies, including spare parts (1) $ 34,680 $ 28,590 Work in process (2) 41,367 27,212 Finished goods 1,132 1,752 Total current inventories 77,179 57,554 Add: Non-current portion (3) 12,589 5,744 Total inventories $ 89,768 $ 63,298 (1) Includes raw materials to support activities pertaining to the Company’s rare earth metal, alloy and magnet manufacturing capabilities. (2) Includes packaged and finished NdPr oxide shipped to the Company’s toller for processing into NdPr metal. (3) Represents stockpiled ore that is not expected to be processed within the next 12 months as well as certain raw materials that are not expected to be consumed within the next 12 months.
Schedule of Noncurrent Inventories	The Company’s inventories consisted of the following: September 30, 2023 December 31, 2022 (in thousands) Raw materials and supplies, including spare parts (1) $ 34,680 $ 28,590 Work in process (2) 41,367 27,212 Finished goods 1,132 1,752 Total current inventories 77,179 57,554 Add: Non-current portion (3) 12,589 5,744 Total inventories $ 89,768 $ 63,298 (1) Includes raw materials to support activities pertaining to the Company’s rare earth metal, alloy and magnet manufacturing capabilities. (2) Includes packaged and finished NdPr oxide shipped to the Company’s toller for processing into NdPr metal. (3) Represents stockpiled ore that is not expected to be processed within the next 12 months as well as certain raw materials that are not expected to be consumed within the next 12 months.

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Tables)	9 Months Ended
	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Schedule of Property, Plant and Equipment and Depreciation and Depletion Expense	The Company’s property, plant and equipment consisted of the following: September 30, 2023 December 31, 2022 (in thousands) Land and land improvements $ 16,425 $ 16,102 Buildings and building improvements 25,427 15,111 Machinery and equipment 473,578 186,388 Assets under construction 240,219 338,482 Mineral rights 438,395 438,395 Property, plant and equipment, gross 1,194,044 994,478 Less: Accumulated depreciation and depletion (96,317) (58,735) Property, plant and equipment, net $ 1,097,727 $ 935,743 The Company’s depreciation and depletion expense were as follows: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Depreciation expense (1) $ 13,951 $ (656) $ 28,385 $ 3,702 Depletion expense $ 2,664 $ 2,664 $ 8,407 $ 8,808 (1) As noted above, during the three months ended September 30, 2022, the Company recorded a reduction to depreciation expense, reflecting the excess of the asset retirement obligation decrement over the carrying amount of the related property, plant and equipment, as a result of changes in the Company’s estimates of cash flows underlying its asset retirement obligations.

INTANGIBLE ASSETS (Tables)

INTANGIBLE ASSETS (Tables)	9 Months Ended
	Sep. 30, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets	The Company’s intangible assets were as follows: September 30, 2023 December 31, 2022 (in thousands) Intangible assets with indefinite lives: Emissions allowances $ 316 $ 89 Intangible assets with definite lives: Patent and intellectual property license 8,963 — Less: Accumulated amortization (100) — Patent and intellectual property license, net 8,863 — Intangible assets, net $ 9,179 $ 89
Schedule of Indefinite-Lived Intangible Assets	The Company’s intangible assets were as follows: September 30, 2023 December 31, 2022 (in thousands) Intangible assets with indefinite lives: Emissions allowances $ 316 $ 89 Intangible assets with definite lives: Patent and intellectual property license 8,963 — Less: Accumulated amortization (100) — Patent and intellectual property license, net 8,863 — Intangible assets, net $ 9,179 $ 89
Schedule of Future Amortization Expense	The following table presents the estimated amortization expense based on amortizing intangible assets as of September 30, 2023: (in thousands) Period: Remainder of 2023 $ 299 2024 1,195 2025 1,195 2026 1,195 2027 1,195 Thereafter 3,784 Total $ 8,863

DEBT OBLIGATIONS (Tables)

DEBT OBLIGATIONS (Tables)	9 Months Ended
	Sep. 30, 2023
Debt Disclosure [Abstract]
Schedule of Long-term Debt Obligations	The Company’s long-term debt was as follows: September 30, 2023 December 31, 2022 (in thousands) Convertible Notes due 2026 $ 690,000 $ 690,000 Less: Unamortized debt issuance costs (8,906) (11,556) Long-term debt, net $ 681,094 $ 678,444 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: September 30, 2023 December 31, 2022 (in thousands) Equipment notes Current $ 2,193 $ 2,392 Non-current 3,147 4,743 $ 5,340 $ 7,135
Schedule of Interest Expense, Net	Interest expense related to the Convertible Notes was as follows: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Coupon interest $ 431 $ 431 $ 1,293 $ 1,293 Amortization of debt issuance costs 884 881 2,650 2,637 Convertible Notes interest expense $ 1,315 $ 1,312 $ 3,943 $ 3,930

LEASES (Tables)

LEASES (Tables)	9 Months Ended
	Sep. 30, 2023
Leases [Abstract]
Schedule of Maturities of Operating Lease Liability	As of September 30, 2023, the maturities of the Company’s operating and finance lease liabilities were as follows: (in thousands) Operating Leases Finance Leases Period: Remainder of 2023 $ 162 $ 56 2024 1,422 228 2025 1,441 179 2026 1,337 59 2027 1,370 54 Thereafter 4,066 160 Total lease payments 9,798 736 Less: Imputed interest (2,056) (108) Total $ 7,742 $ 628
Schedule of Maturities of Finance Lease Liability	As of September 30, 2023, the maturities of the Company’s operating and finance lease liabilities were as follows: (in thousands) Operating Leases Finance Leases Period: Remainder of 2023 $ 162 $ 56 2024 1,422 228 2025 1,441 179 2026 1,337 59 2027 1,370 54 Thereafter 4,066 160 Total lease payments 9,798 736 Less: Imputed interest (2,056) (108) Total $ 7,742 $ 628
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 September 30, 2023 December 31, 2022 (in thousands) Operating Leases: Right-of-use assets Operating lease right-of-use assets $ 10,346 $ 99 Operating lease liability, current Operating lease liabilities (included in current liabilities) $ 728 $ 84 Operating lease liability, non-current Operating lease liabilities (included in non-current liabilities) 7,014 15 Total operating lease liabilities $ 7,742 $ 99 Finance Leases: Right-of-use assets Other non-current assets $ 650 $ 451 Finance lease liability, current Other current liabilities $ 197 $ 354 Finance lease liability, non-current Other non-current liabilities 431 242 Total finance lease liabilities $ 628 $ 596

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	9 Months Ended
	Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Stock Awards Activity	The Company’s stock-based compensation was recorded as follows: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Cost of sales $ 842 $ 889 $ 2,759 $ 2,110 Selling, general and administrative 5,193 6,912 15,603 22,717 Advanced projects, start-up, development and other 263 5 679 192 Total stock-based compensation expense $ 6,298 $ 7,806 $ 19,041 $ 25,019 Stock-based compensation capitalized to property, plant and equipment, net $ 367 $ 267 $ 1,566 $ 951

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2023
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The carrying amounts and estimated fair values by input level of the Company’s financial instruments were as follows: September 30, 2023 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 547,668 $ 547,668 $ 547,668 $ — $ — Short-term investments $ 536,994 $ 536,994 $ 536,994 $ — $ — Restricted cash $ 1,575 $ 1,575 $ 1,575 $ — $ — Financial liabilities: Convertible Notes $ 681,094 $ 591,923 $ 591,923 $ — $ — Equipment notes $ 5,340 $ 5,142 $ — $ 5,142 $ — December 31, 2022 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 136,627 $ 136,627 $ 136,627 $ — $ — Short-term investments $ 1,045,718 $ 1,045,718 $ 1,045,718 $ — $ — Restricted cash $ 6,882 $ 6,882 $ 6,882 $ — $ — Financial liabilities: Convertible Notes $ 678,444 $ 610,650 $ 610,650 $ — $ — Equipment notes $ 7,135 $ 6,807 $ — $ 6,807 $ —
Fair Value Disclosure of Asset and Liability Not Measured at Fair Value	The carrying amounts and estimated fair values by input level of the Company’s financial instruments were as follows: September 30, 2023 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 547,668 $ 547,668 $ 547,668 $ — $ — Short-term investments $ 536,994 $ 536,994 $ 536,994 $ — $ — Restricted cash $ 1,575 $ 1,575 $ 1,575 $ — $ — Financial liabilities: Convertible Notes $ 681,094 $ 591,923 $ 591,923 $ — $ — Equipment notes $ 5,340 $ 5,142 $ — $ 5,142 $ — December 31, 2022 (in thousands) Carrying Amount Fair Value Level 1 Level 2 Level 3 Financial assets: Cash and cash equivalents $ 136,627 $ 136,627 $ 136,627 $ — $ — Short-term investments $ 1,045,718 $ 1,045,718 $ 1,045,718 $ — $ — Restricted cash $ 6,882 $ 6,882 $ 6,882 $ — $ — Financial liabilities: Convertible Notes $ 678,444 $ 610,650 $ 610,650 $ — $ — Equipment notes $ 7,135 $ 6,807 $ — $ 6,807 $ —

EARNINGS (LOSS) PER SHARE (Tabl

EARNINGS (LOSS) PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Schedule of Weighted Average Number of Shares	The following table reconciles the weighted-average common shares outstanding used in the calculation of basic earnings (loss) per share to the weighted-average common shares outstanding used in the calculation of diluted earnings (loss) per share: For the three months ended September 30, For the nine months ended September 30, 2023 2022 2023 2022 Weighted-average shares outstanding, basic 177,231,717 176,543,624 177,034,068 176,476,276 Assumed conversion of Convertible Notes — 15,584,409 15,584,409 15,584,409 Assumed conversion of restricted stock — 840,786 620,190 944,925 Assumed conversion of RSUs — 441,038 393,995 433,329 Weighted-average shares outstanding, diluted 177,231,717 193,409,857 193,632,662 193,438,939
Schedule of Unweighted Potentially Dilutive Securities	The following table presents unweighted potentially dilutive shares that were not included in the computation of diluted earnings (loss) per share because to do so would have been antidilutive: For the three months ended September 30, For the nine months ended September 30, 2023 2022 2023 2022 Convertible Notes 15,584,409 — — — Restricted Stock 685,202 — — — RSUs 1,629,938 6,013 3,184 6,013
Schedule Of Potentially Dilutive Securities	The following table presents the calculation of basic and diluted earnings (loss) per share for the Company’s common stock: For the three months ended September 30, For the nine months ended September 30, (in thousands, except share and per share data) 2023 2022 2023 2022 Calculation of basic earnings (loss) per share: Net income (loss) $ (4,276) $ 63,177 $ 40,566 $ 221,997 Weighted-average shares outstanding, basic 177,231,717 176,543,624 177,034,068 176,476,276 Basic earnings (loss) per share $ (0.02) $ 0.36 $ 0.23 $ 1.26 Calculation of diluted earnings (loss) per share: Net income (loss) $ (4,276) $ 63,177 $ 40,566 $ 221,997 Interest expense, net of tax (1) : Convertible Notes — 985 2,977 2,967 Diluted income (loss) $ (4,276) $ 64,162 $ 43,543 $ 224,964 Weighted-average shares outstanding, diluted 177,231,717 193,409,857 193,632,662 193,438,939 Diluted earnings (loss) per share $ (0.02) $ 0.33 $ 0.22 $ 1.16 (1) The nine months ended September 30, 2023, was tax-effected at a rate of 24.5%, and the three and nine months ended September 30, 2022, were tax-effected at a rate of 24.9% and 24.5%, respectively.

RELATED PARTY TRANSACTIONS (Tab

RELATED PARTY TRANSACTIONS (Tables)	9 Months Ended
	Sep. 30, 2023
Related Party Transactions [Abstract]
Schedule of Related Party Revenue and Cost of Sales	The Company’s related-party revenue and cost of sales were as follows: For the three months ended September 30, For the nine months ended September 30, (in thousands) 2023 2022 2023 2022 Revenue: Rare earth concentrate $ 51,502 $ 114,894 $ 203,186 $ 401,496 Other rare earth products (1) $ — $ 172 $ — $ 8,646 Cost of sales (2) $ 21,829 $ 21,842 $ 66,817 $ 65,368 (1) Represents sales agreements with Shenghe for non-concentrate products, including certain stockpiles of rare earth fluoride. (2) Excludes depreciation, depletion and amortization and includes shipping and freight.

SUPPLEMENTAL CASH FLOW INFORM_2

SUPPLEMENTAL CASH FLOW INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2023
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 nine months ended September 30, (in thousands) 2023 2022 Supplemental cash flow information: Cash paid for interest $ 1,116 $ 1,140 Cash payments related to income taxes $ 23,101 $ 16,827 Change in construction payables $ 10,952 $ 35,779 Supplemental non-cash investing and financing activities: Common stock issued to acquire intangible asset $ 8,963 $ — Operating ROU assets obtained in exchange for lease liabilities $ 7,608 $ 168 Revenue recognized in exchange for debt principal reduction $ — $ 13,566 Decrease in estimates of asset retirement costs $ — $ 10,395

DESCRIPTION OF BUSINESS AND B_2

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Details)	9 Months Ended
	Sep. 30, 2023 segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of reportable segments	1

SIGNIFICANT ACCOUNTING POLICI_3

SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Concentration Risk [Line Items]
Impairment of intangible assets	$ 0	$ 0	$ 0	$ 0
Impairment charges, operating lease	0	0	0	0
Impairment charges, finance lease	$ 0	$ 0	$ 0	$ 0
Shenghe | Product sales | Customer concentration risk | Shenghe
Concentration Risk [Line Items]
Concentration risk percentage			90%

CASH, CASH EQUIVALENTS AND IN_3

CASH, CASH EQUIVALENTS AND INVESTMENTS - Amortized Costs, Unrealized Gains and Losses, and Estimated Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Total cash and equivalents
Amortized Cost Basis	$ 547,614	$ 136,628
Unrealized Gains	58	1
Unrealized Losses	(4)	(2)
Estimated Fair Value	547,668	136,627
Short-term investments:
Amortized Cost Basis	537,090	1,045,464
Unrealized Gains	62	362
Unrealized Losses	(158)	(108)
Short-term investments	536,994	1,045,718
Amortized Cost Basis	1,084,704	1,182,092
Unrealized Gains	120	363
Unrealized Losses	(162)	(110)
Total cash, cash equivalents and short-term investments	1,084,662	1,182,345
U.S. agency securities
Short-term investments:
Amortized Cost Basis	141,873	979,878
Unrealized Gains	1	361
Unrealized Losses	(155)	(17)
Short-term investments	141,719	980,222
U.S. Treasury securities
Short-term investments:
Amortized Cost Basis	395,217	65,586
Unrealized Gains	61	1
Unrealized Losses	(3)	(91)
Short-term investments	395,275	65,496
Demand deposits
Total cash and equivalents
Amortized Cost Basis	1,580	7,373
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	1,580	7,373
Total cash equivalents
Total cash and equivalents
Amortized Cost Basis	546,034	129,255
Unrealized Gains	58	1
Unrealized Losses	(4)	(2)
Estimated Fair Value	546,088	129,254
Money market funds
Total cash and equivalents
Amortized Cost Basis	134,038	64,855
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	134,038	64,855
U.S. agency securities
Total cash and equivalents
Amortized Cost Basis	0	63,605
Unrealized Gains	0	1
Unrealized Losses	0	(2)
Estimated Fair Value	0	63,604
U.S. Treasury securities
Total cash and equivalents
Amortized Cost Basis	327,224	795
Unrealized Gains	48	0
Unrealized Losses	(4)	0
Estimated Fair Value	327,268	795
Commercial paper
Total cash and equivalents
Amortized Cost Basis	49,662	0
Unrealized Gains	7	0
Unrealized Losses	0	0
Estimated Fair Value	49,669	0
Certificates of deposit
Total cash and equivalents
Amortized Cost Basis	35,110	0
Unrealized Gains	3	0
Unrealized Losses	0	0
Estimated Fair Value	$ 35,113	$ 0

CASH, CASH EQUIVALENTS AND IN_4

CASH, CASH EQUIVALENTS AND INVESTMENTS - Debt Securities, Income and Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Gross realized gains	$ 1	$ 71	$ 506	$ 71
Gross realized losses	0	199	139	199
Interest and investment income	$ 14,455	$ 6,274	$ 41,607	$ 8,529

CASH, CASH EQUIVALENTS AND IN_5

CASH, CASH EQUIVALENTS AND INVESTMENTS - Schedule of Investments Classified by Contractual Maturity Date (Details) $ in Thousands	Sep. 30, 2023 USD ($)
Debt Securities, Available-for-Sale, Fair Value, Fiscal Year Maturity [Abstract]
Due within one year	$ 926,223
Due after one year through two years	22,821
Total	$ 949,044

INVENTORIES (Details)

INVENTORIES (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Inventory Disclosure [Abstract]
Raw materials and supplies, including spare parts	$ 34,680	$ 28,590
Work in process	41,367	27,212
Finished goods	1,132	1,752
Total current inventories	77,179	57,554
Add: Non-current portion	12,589	5,744
Total inventories	$ 89,768	$ 63,298

PROPERTY, PLANT AND EQUIPMENT -

PROPERTY, PLANT AND EQUIPMENT - Schedule Of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,194,044	$ 994,478
Less: Accumulated depreciation and depletion	(96,317)	(58,735)
Property, plant and equipment, net	1,097,727	935,743
Land and land improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	16,425	16,102
Buildings and building improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	25,427	15,111
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	473,578	186,388
Assets under construction
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	240,219	338,482
Mineral rights
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 438,395	$ 438,395

PROPERTY, PLANT AND EQUIPMENT_2

PROPERTY, PLANT AND EQUIPMENT - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($) a	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) a	Sep. 30, 2022 USD ($)	Feb. 28, 2022 USD ($)	Nov. 30, 2020 USD ($)
Property, Plant and Equipment [Line Items]
Capitalized expenditures			$ 199,900,000	$ 250,100,000
Assets transferred			248,400,000
Technology investment agreement, stage II optimization contribution	$ 100,000		100,000			$ 9,600,000
Proceeds from technology investment agreement, stage II optimization contribution			0	5,100,000
HREE Production Project Agreement, stage II optimization contribution					$ 35,000,000
Proceeds from HREE Production Project Agreement, contribution			1,100,000
Decrease in property, plant and equipment		$ 10,400,000		10,400,000
Decrease in depreciation expense		2,700,000		2,700,000
Demolition costs	800,000		5,500,000
Asset impairment charges	$ 0	0	0	$ 0
Machinery and equipment
Property, Plant and Equipment [Line Items]
Assets transferred			$ 239,800,000
Decrease in property, plant and equipment		2,700,000
Buildings and building improvements
Property, Plant and Equipment [Line Items]
Decrease in property, plant and equipment		600,000
Assets under construction
Property, Plant and Equipment [Line Items]
Decrease in property, plant and equipment		$ 6,700,000
Texas
Property, Plant and Equipment [Line Items]
Area of real estate property | a	18		18

PROPERTY, PLANT AND EQUIPENT -

PROPERTY, PLANT AND EQUIPENT - Depreciation and Depletion Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 13,951	$ (656)	$ 28,385	$ 3,702
Depletion expense	$ 2,664	$ 2,664	$ 8,407	$ 8,808

INTANGIBLE ASSETS - Additional

INTANGIBLE ASSETS - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 31, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Consulting agreement, expected service fee	$ 15
Consulting agreement, expected service fee, payment period	4 years
Amortization expense		$ 0.1	$ 0	$ 0.1	$ 0
Licensing Agreement
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Stock to be issued, purchase of assets (in shares)	435,729
Common stock issued to acquire intangible asset (in share)	152,504
Definite-lived intangible asset	$ 9
Intangible asset, useful life	7 years 6 months
Licensing Agreement | First vesting period
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Stock to be issued, purchase of assets (in shares)	43,573
Licensing Agreement | Second vesting period
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Stock to be issued, purchase of assets (in shares)	43,573
Licensing Agreement | Third vesting period
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Stock to be issued, purchase of assets (in shares)	43,573
Licensing Agreement | Fourth vesting period
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets [Line Items]
Stock to be issued, purchase of assets (in shares)	152,506

INTANGIBLE ASSETS - Finite-Live

INTANGIBLE ASSETS - Finite-Lived and Indefinite-Lived Intangible Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Intangible assets with indefinite lives:
Emissions allowances	$ 316	$ 89
Intangible assets with definite lives:
Patent and intellectual property license	8,963	0
Less: Accumulated amortization	(100)	0
Total	8,863	0
Intangible assets, net	$ 9,179	$ 89

INTANGIBLE ASSETS - Remaining A

INTANGIBLE ASSETS - Remaining Amortization Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Goodwill and Intangible Assets Disclosure [Abstract]
Remainder of 2023	$ 299
2024	1,195
2025	1,195
2026	1,195
2027	1,195
Thereafter	3,784
Total	$ 8,863	$ 0

ASSET RETIREMENT AND ENVIRONM_2

ASSET RETIREMENT AND ENVIRONMENTAL OBLIGATIONS (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Unusual Risk or Uncertainty [Line Items]
ARO decrement	$ 13.1		$ 13.1
Decrease in property, plant and equipment	10.4		10.4
Decrease in depreciation expense	$ 2.7		$ 2.7
Asset retirement obligation, current		$ 0.2		$ 0.2
Estimated undiscounted cash flows, to satisfy obligation		$ 50.3		50.4
Remediation term		24 years
Discount rate		2.93%
Environmental obligations, undiscounted cost		$ 26.8		27.2
Environmental obligations, current		0.5		0.5
Closure and reclamation obligations, financial assurances		$ 45.4		$ 43.5
Minimum
Unusual Risk or Uncertainty [Line Items]
Asset retirement obligations, credit-adjusted risk free rate		6.50%
Maximum
Unusual Risk or Uncertainty [Line Items]
Asset retirement obligations, credit-adjusted risk free rate		12%

DEBT OBLIGATIONS - Schedule of

DEBT OBLIGATIONS - Schedule of Long-term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Less: Unamortized debt issuance costs	$ (8,906)	$ (11,556)
Long-term debt, net	681,094	678,444
Convertible Notes due 2026 | Convertible Notes
Debt Instrument [Line Items]
Outstanding balance, gross	$ 690,000	$ 690,000

DEBT OBLIGATIONS - Convertible

DEBT OBLIGATIONS - Convertible Notes (Details) - Convertible Notes due 2026 - Convertible Notes $ / shares in Units, $ in Millions	1 Months Ended	9 Months Ended
	Mar. 31, 2021 USD ($) $ / shares	Sep. 30, 2023 USD ($) shares
Debt Instrument [Line Items]
Advance funded	$ 690
Interest rate	0.25%
Debt instrument, convertible, conversion price (in USD 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
If-converted value in excess of principal		$ 0
Effective interest rate		0.51%
Debt term		2 years 6 months
Maximum
Debt Instrument [Line Items]
Debt instrument, convertible, conversion ratio	0.0285714

DEBT OBLIGATIONS - Interest Exp

DEBT OBLIGATIONS - Interest Expense, Net (Details) - Convertible Notes due 2026 - Convertible Notes - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Debt Instrument [Line Items]
Coupon interest	$ 431	$ 431	$ 1,293	$ 1,293
Amortization of debt issuance costs	884	881	2,650	2,637
Convertible Notes interest expense	$ 1,315	$ 1,312	$ 3,943	$ 3,930

DEBT OBLIGATIONS - Equipment No

DEBT OBLIGATIONS - Equipment Notes (Details) - Equipment notes - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022
Equipment notes
Current	$ 2,193	$ 2,392
Non-current	3,147	4,743
Notes payable	$ 5,340	$ 7,135
Minimum
Debt Instrument [Line Items]
Debt term	4 years
Interest rate	0%
Maximum
Debt Instrument [Line Items]
Debt term	5 years
Interest rate	6.50%

LEASES - Additional Information

LEASES - Additional Information (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2023 USD ($) renewalOption	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Leases [Abstract]
Total	$ 7,300	$ 7,742	$ 99
Payments for tenant improvements	$ 2,900
Initial term	91 months
Number of renewal options | renewalOption	1
Renewal options term	5 years
Annual base rent	$ 1,200
Operating lease right-of-use assets	$ 10,300	$ 10,346	$ 99

LEASES - Maturities of Lease Li

LEASES - Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Operating Leases
Remainder of 2023	$ 162
2024	1,422
2025	1,441
2026	1,337
2027	1,370
Thereafter	4,066
Total lease payments	9,798
Less: Imputed interest	(2,056)
Total	7,742	$ 7,300	$ 99
Finance Leases
Remainder of 2023	56
2024	228
2025	179
2026	59
2027	54
Thereafter	160
Total lease payments	736
Less: Imputed interest	(108)
Total	$ 628		$ 596

LEASES - Supplemental Disclosur

LEASES - Supplemental Disclosure for the Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Right-of-use assets
Right-of-use assets	$ 10,346	$ 10,300	$ 99
Operating lease liability, current	728		84
Operating lease liability, non-current	7,014		15
Total operating lease liabilities	7,742	$ 7,300	99
Finance Leases:
Right-of-use assets	650		451
Finance lease liability, current	197		354
Finance lease liability, non-current	431		242
Total finance lease liabilities	$ 628		$ 596
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other non-current assets		Other non-current assets
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other current liabilities		Other current liabilities
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other non-current liabilities		Other non-current liabilities

INCOME TAXES (Details)

INCOME TAXES (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Effective tax rate	4.50%	24.90%	24.50%	24.50%

STOCK-BASED COMPENSATION - Addi

STOCK-BASED COMPENSATION - Additional Information (Details)	9 Months Ended
	Sep. 30, 2023 shares
2020 Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants (in shares)	6,101,859
2023 Performance Share Plan | Market-Based PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted (in shares)	62,709
Vesting period	3 years
Requisite service period	3 years
2023 Performance Share Plan | Market-Based PSUs | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage of the awards granted (as a percent)	0%
2023 Performance Share Plan | Market-Based PSUs | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage of the awards granted (as a percent)	200%

STOCK-BASED COMPENSATION - Sche

STOCK-BASED COMPENSATION - Schedule of Stock-Based Compensation and Related Income Tax Benefit (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 6,298	$ 7,806	$ 19,041	$ 25,019
Stock-based compensation capitalized to property, plant and equipment, net	367	267	1,566	951
Cost of sales
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	842	889	2,759	2,110
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	5,193	6,912	15,603	22,717
Advanced projects, start-up, development and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 263	$ 5	$ 679	$ 192

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financial assets:
Cash and cash equivalents	$ 547,668	$ 136,627
Level 1
Financial assets:
Cash and cash equivalents	547,668	136,627
Short-term investments	536,994	1,045,718
Restricted cash	1,575	6,882
Level 1 | Convertible Notes
Financial liabilities:
Debt fair value	591,923	610,650
Level 1 | Equipment notes
Financial liabilities:
Debt fair value	0	0
Level 2
Financial assets:
Cash and cash equivalents	0	0
Short-term investments	0	0
Restricted cash	0	0
Level 2 | Convertible Notes
Financial liabilities:
Debt fair value	0	0
Level 2 | Equipment notes
Financial liabilities:
Debt fair value	5,142	6,807
Level 3
Financial assets:
Cash and cash equivalents	0	0
Short-term investments	0	0
Restricted cash	0	0
Level 3 | Convertible Notes
Financial liabilities:
Debt fair value	0	0
Level 3 | Equipment notes
Financial liabilities:
Debt fair value	0	0
Carrying Amount
Financial assets:
Cash and cash equivalents	547,668	136,627
Short-term investments	536,994	1,045,718
Restricted cash	1,575	6,882
Carrying Amount | Convertible Notes
Financial liabilities:
Debt fair value	681,094	678,444
Carrying Amount | Equipment notes
Financial liabilities:
Debt fair value	5,340	7,135
Fair Value
Financial assets:
Cash and cash equivalents	547,668	136,627
Short-term investments	536,994	1,045,718
Restricted cash	1,575	6,882
Fair Value | Convertible Notes
Financial liabilities:
Debt fair value	591,923	610,650
Fair Value | Equipment notes
Financial liabilities:
Debt fair value	$ 5,142	$ 6,807

EARNINGS (LOSS) PER SHARE - Sch

EARNINGS (LOSS) PER SHARE - Schedule of Weighted Average Number of Shares (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Class of Warrant or Right [Line Items]
Weighted-average shares outstanding, basic (in shares)	177,231,717	176,543,624	177,034,068	176,476,276
Assumed conversion of Convertible Notes (in shares)	0	15,584,409	15,584,409	15,584,409
Weighted-average shares outstanding, diluted (in shares)	177,231,717	193,409,857	193,632,662	193,438,939
Restricted Stock
Class of Warrant or Right [Line Items]
Assumed conversion of restricted stock awards (in shares)	0	840,786	620,190	944,925
RSUs
Class of Warrant or Right [Line Items]
Assumed conversion of restricted stock awards (in shares)	0	441,038	393,995	433,329

EARNINGS (LOSS) PER SHARE - S_2

EARNINGS (LOSS) PER SHARE - Schedule of Unweighted Potentially Dilutive Shares (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Convertible Notes
Class of Warrant or Right [Line Items]
Antidilutive securities excluding from computation (in shares)	15,584,409	0	0	0
Restricted Stock
Class of Warrant or Right [Line Items]
Antidilutive securities excluding from computation (in shares)	685,202	0	0	0
RSUs
Class of Warrant or Right [Line Items]
Antidilutive securities excluding from computation (in shares)	1,629,938	6,013	3,184	6,013

EARNINGS (LOSS) PER SHARE - Cal

EARNINGS (LOSS) PER SHARE - Calculation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Calculation of basic earnings (loss) per share:
Net income (loss)	$ (4,276)	$ 63,177	$ 40,566	$ 221,997
Weighted-average shares outstanding, basic (in shares)	177,231,717	176,543,624	177,034,068	176,476,276
Basic earnings (loss) per share (in USD per share)	$ (0.02)	$ 0.36	$ 0.23	$ 1.26
Calculation of diluted earnings (loss) per share:
Interest expense on convertible debt, net of tax	$ 0	$ 985	$ 2,977	$ 2,967
Diluted income (loss)	$ (4,276)	$ 64,162	$ 43,543	$ 224,964
Weighted-average shares outstanding, diluted (in shares)	177,231,717	193,409,857	193,632,662	193,438,939
Diluted earnings (loss) per share (in USD per share)	$ (0.02)	$ 0.33	$ 0.22	$ 1.16
Effective tax rate	4.50%	24.90%	24.50%	24.50%

RELATED PARTY TRANSACTIONS - Ad

RELATED PARTY TRANSACTIONS - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Oct. 31, 2023	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Related Party Transaction [Line Items]
Purchases from related party			$ 5,800	$ 15,300	$ 7,600	$ 18,500
Accounts receivable			13,180		13,180		$ 32,856
Related party
Related Party Transaction [Line Items]
Accounts receivable			$ 11,900		$ 11,900		$ 29,800
Offtake Agreement
Related Party Transaction [Line Items]
Initial term		2 years
Extension period		1 year
VREX Tolling Agreement | Subsequent event
Related Party Transaction [Line Items]
Initial term	3 years
Extension period	3 years

RELATED PARTY TRANSACTIONS - Re

RELATED PARTY TRANSACTIONS - Related Party Revenue and Cost of Sales (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Related Party Transaction [Line Items]
Total revenue	$ 52,516	$ 124,445	$ 212,240	$ 434,265
Cost of sales	22,217	22,417	69,137	67,682
Related party
Related Party Transaction [Line Items]
Cost of sales	21,829	21,842	66,817	65,368
Rare earth concentrate
Related Party Transaction [Line Items]
Total revenue	52,472	124,231	212,139	425,169
Rare earth concentrate | Related party
Related Party Transaction [Line Items]
Total revenue	51,502	114,894	203,186	401,496
Other rare earth products
Related Party Transaction [Line Items]
Total revenue	44	214	101	9,096
Other rare earth products | Related party
Related Party Transaction [Line Items]
Total revenue	$ 0	$ 172	$ 0	$ 8,646

SUPPLEMENTAL CASH FLOW INFORM_3

SUPPLEMENTAL CASH FLOW INFORMATION (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Supplemental cash flow information:
Cash paid for interest	$ 1,116	$ 1,140
Cash payments related to income taxes	23,101	16,827
Change in construction payables	10,952	35,779
Supplemental non-cash investing and financing activities:
Common stock issued to acquire intangible asset	8,963	0
Operating ROU assets obtained in exchange for lease liabilities	7,608	168
Revenue recognized in exchange for debt principal reduction	0	13,566
Decrease in estimates of asset retirement costs	$ 0	$ 10,395