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                                                                 EXHIBIT 3(a)

              AMENDED CERTIFICATE OF DESIGNATION, PREFERENCES AND
                    RIGHTS OF SERIES A JUNIOR PARTICIPATING
                      PREFERRED STOCK OF CABOT CORPORATION

                            (Pursuant to Section 151
            of the General Corporation Law of the State of Delaware)

                  We, Kennett F. Burnes, President, and Charles D. Gerlinger,
Secretary of Cabot Corporation (the "Corporation"), a corporation organized and
existing under the General Corporation Law of the State of Delaware, in
accordance with the provisions of Section 103 thereof, DO HEREBY CERTIFY as
follows:

                  That pursuant to the authority conferred upon the Board of
Directors by the Certificate of Incorporation of the said Corporation, said
Board of Directors on November 10, 1995, voted to create a series of 1,000,000
shares of Preferred Stock designated as Series A Junior Participating Preferred
Stock:

                  VOTED, that pursuant to the authority granted to and vested in
the Board of Directors of this Corporation in accordance with the provisions of
the Corporation's Certificate of Incorporation and Section 151(g) of the General
Corporation Law of the State of Delaware, the Board of Directors hereby approves
and adopts an amendment to the Certificate of Designation, Preferences and
Rights of the Series A Junior Participating Preferred Stock of Cabot
Corporation, which Certificate is hereby amended in its entirety, and hereby
states the designation and number of shares, and fixes the relative rights,
preferences and limitations thereof (in addition to the provisions set forth in
the Corporation's Certificate of Incorporation which are applicable to the
Preferred Stock of all classes and series) as follows:

                  Section 1. Designation and Amount. There shall be a series of
Preferred Stock, par value $1.00 per share, of the Corporation which shall be
designated as "Series A Junior Participating Preferred Stock," par value $1.00
per share, and the number of shares constituting such series shall be 1,000,000.
Such number of shares may be increased or decreased by resolution of the Board
of Directors; provided, that no decrease shall reduce the number of shares of
Series A Junior Participating Preferred Stock to a number less than that of the
shares then outstanding plus the number of shares issuable upon exercise of
outstanding rights, options or warrants or upon conversion of outstanding
securities issued by the Corporation.

                  Section 2.  Dividends and Distributions.

                  (A) Subject to the prior and superior rights of the holders of
any shares of any series of Preferred Stock ranking prior and superior to the
Series A Junior Participating Preferred Stock with respect to dividends, the
holders of shares of Series A
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Junior Participating Preferred Stock in preference to the holders of shares of
Common Stock, par value $1.00 per share (the "Common Stock"), of the Corporation
and any other junior stock, shall be entitled to receive, when, as and if
declared by the Board of Directors out of funds legally available for the
purpose, quarterly dividends payable in cash on the last day of each fiscal
quarter of the Corporation in each year or such other dates as the Board of
Directors of the Corporation shall approve (each such date being referred to
herein as a "Quarterly Dividend Payment Date"), commencing on the first
Quarterly Dividend Payment Date after the first issuance of a share or fraction
of a share of Series A Junior Participating Preferred Stock in an amount per
share (rounded to the nearest cent) equal to the greater of (a) $18.00 or (b)
subject to the provision for adjustment hereinafter set forth, 100 times the
aggregate per share amount of all cash dividends, and 100 times the aggregate
per share amount (payable in kind) of all non-cash dividends or other
distributions other than a dividend payable in shares of Common Stock or a
subdivision of the outstanding shares of Common Stock (by reclassification or
otherwise), declared on the Common Stock since the immediately preceding
Quarterly Dividend Payment Date, or, with respect to the first Quarterly
Dividend Payment Date, since the first issuance of any share or fraction of a
share of Series A Junior Participating Preferred Stock. In the event the
Corporation shall at any time after November 24, 1995 (the "Rights Declaration
Date") (i) declare any dividend on Common Stock payable in shares of Common
Stock, (ii) subdivide (by a stock split or otherwise) the outstanding Common
Stock, or (iii) combine (by a reverse stock split or otherwise) the outstanding
Common Stock into a smaller number of shares, then in each such case the amount
to which holders of shares of Series A Junior Participating Preferred Stock were
entitled immediately prior to such event under clause (b) of the preceding
sentence shall be adjusted by multiplying such amount by a fraction the
numerator of which is the number of shares of Common Stock outstanding
immediately after such event and the denominator of which is the number of
shares of Common Stock that were outstanding immediately prior to such event.

                  (B) The Corporation shall declare a dividend or distribution
on the Series A Junior Participating Preferred Stock as provided in paragraph
(A) above at the time it declares a dividend or distribution on the Common Stock
(other than a dividend payable in shares of Common Stock); provided that, in the
event no dividend or distribution shall have been declared on the Common Stock
during the period between any Quarterly Dividend Payment Date and the next
subsequent Quarterly Dividend Payment Date, a dividend of $18.00 per share on
the Series A Junior Participating Preferred Stock shall nevertheless be payable
on such subsequent Quarterly Dividend Payment Date.

                  (C) So long as any shares of the Series A Junior Participating
Preferred Stock are outstanding, no dividends or other distributions shall be
declared, paid or distributed, or set aside for payment or distribution, on the
Common Stock unless, in each

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case, the dividend required by this Section 2 to be declared on the Series A
Junior Participating Preferred Stock shall have been declared.

                  (D) The holders of the shares of the Series A Junior
Participating Preferred Stock shall not be entitled to receive any dividends or
other distributions except as provided herein.

                  (E) Dividends shall begin to accrue and be cumulative on
outstanding shares of Series A Junior Participating Preferred Stock from the
Quarterly Dividend Payment Date next preceding the date of issue of such shares
of Series A Junior Participating Preferred Stock unless the date of issue of
such shares is prior to the record date for the first Quarterly Dividend Payment
Date, in which case dividends on such shares shall begin to accrue from the date
of issue of such shares, or unless the date of issue is a Quarterly Dividend
Payment Date or is a date after the record date for the determination of holders
of shares of Series A Junior Participating Preferred Stock entitled to receive a
quarterly dividend and before such Quarterly Dividend Payment Date in either of
which events such dividends shall begin to accrue and be cumulative from such
Quarterly Dividend Payment Date. Accrued but unpaid dividends shall not bear
interest. Dividends paid on the shares of Series A Junior Participating
Preferred Stock in an amount less than the total of such dividends at the time
accrued and payable on such shares shall be allocated pro rata on a
share-by-share basis among all such shares at the time outstanding. The Board of
Directors may fix a record date for the determination of holders of shares of
Series A Junior Participating Preferred Stock entitled to receive payment of a
dividend or distribution declared thereon, which record date shall be no more
than 60 days prior to the date fixed for the payment thereof.

                  Section 3.  Voting Rights.  The holders of shares of Series A
Junior Participating Preferred Stock shall have the following voting rights:

                  (A) Subject to the provision for adjustment hereinafter set
forth, each share of Series A Junior Participating Preferred Stock shall entitle
the holder thereof to 100 votes on all matters submitted to a vote of the
stockholders of the Corporation. In the event the Corporation shall at any time
after the Rights Declaration Date (i) declare any dividend on Common Stock
payable in shares of Common Stock, (ii) subdivide (by a stock split or
otherwise) the outstanding Common Stock, or (iii) combine (by a reverse stock
split or otherwise) the outstanding Common Stock into a smaller number of
shares, then in each such case the number of votes per share to which holders of
shares of Series A Junior Participating Preferred Stock were entitled
immediately prior to such event shall be adjusted by multiplying such number by
a fraction the numerator of which is the number of shares of Common Stock
outstanding immediately after such event and the denominator of which is the
number of shares of Common Stock that were outstanding immediately prior to such
event.

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                  (B) Except as otherwise provided herein or by law, the holders
of shares of Series A Junior Participating Preferred Stock and the holders of
shares of Common Stock shall vote together as one class on all matters submitted
to a vote of stockholders of the Corporation.

                  (C)      (i) If at any time dividends on any Series A Junior
Participating Preferred Stock shall be in arrears in an amount equal to at least
six (6) full quarterly dividends (whether or not declared and whether or not
consecutive) thereon, the occurrence of such contingency shall mark the
beginning of a period (herein called a "default period") which shall extend
until such time when all accrued and unpaid dividends for all previous quarterly
dividend periods and for the current quarterly dividend period on all shares of
Series A Junior Participating Preferred Stock then outstanding shall have been
declared and paid or set apart for payment. During each default period, all
holders of Preferred Stock (including holders of the Series A Junior
Participating Preferred Stock) with dividends in arrears in an amount equal to
at least six (6) full quarterly dividends (whether or not declared and whether
or not consecutive) thereon, voting as a class, irrespective of series, shall
have the right to elect two (2) Directors.

                           (ii) During any default period, such voting right of
the holders of Series A Junior Participating Preferred Stock may be exercised
initially at a special meeting called pursuant to subparagraph (iii) of this
Section 3(C) or at any annual meeting of stockholders, and thereafter at annual
meetings of stockholders, provided that neither such voting right nor the right
of the holders of any other series of Preferred Stock, if any, to increase, in
certain cases, the authorized number of Directors shall be exercised unless the
holders of one-third (1/3) in number of shares of Preferred Stock outstanding
shall be present in person or by proxy. The absence of a quorum of the holders
of Common Stock shall not affect the exercise by the holders of Preferred Stock
of such voting right. At any meeting at which the holders of Preferred Stock
shall exercise such voting right initially during an existing default period,
they shall have the right, voting as a class, to elect Directors to fill such
vacancies, if any, in the Board of Directors as may then exist up to two (2)
Directors or, if such right is exercised at an annual meeting, to elect two (2)
Directors. If the number which may be so elected at any special meeting does not
amount to the required number, the holders of the Preferred Stock shall have the
right to make such increase in the number of Directors as shall be necessary to
permit the election by them of the required number. After the holders of the
Preferred Stock shall have exercised their right to elect Directors in any
default period and during the continuance of such period, the number of
directors shall not be increased or decreased except by vote of the holders of
Preferred Stock as herein provided or pursuant to the rights of any equity
securities ranking senior to or pari passu with the Series A Junior
Participating Preferred Stock.

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                           (iii) Unless the holders of Preferred Stock shall,
during an existing default period, have previously exercised their right to
elect Directors, the Board of Directors may order, or any stockholder or
stockholders owning in the aggregate not less than ten percent (10%) of the
total number of Preferred Stock outstanding, irrespective of series, may
request, the calling of a special meeting of the holders of Preferred Stock,
which meeting shall thereupon be called by the Chairman of the Board or the
President of the Corporation. Notice of such meeting and of any annual meeting
at which holders of Preferred Stock are entitled to vote pursuant to this
paragraph (C)(iii) shall be given to each holder of record of Preferred Stock by
mailing a copy of such notice to him at his last address as the same appears on
the books of the Corporation. Such meeting shall be called for a time not
earlier than 10 days and not later than 60 days after such order or request or
in default of the calling of such meeting within 60 days after such order or
request, such meeting may be called on similar notice by any stockholder or
stockholders owning in the aggregate not less than ten percent (10%) of the
total number of shares of Preferred Stock outstanding. Notwithstanding the
provisions of this paragraph (C)(iii), no such special meeting shall be called
during the period within 60 days immediately preceding the date fixed for the
next annual meeting of the stockholders.

                           (iv)  In any default period, the holders of Common
Stock, and other classes of stock of the Corporation if applicable, shall
continue to be entitled to elect the whole number of Directors until the holders
of Preferred Stock shall have exercised their right to elect two (2) Directors
voting as a class, after the exercise of which right (x) the Directors so
elected by the holders of Preferred Stock shall continue in office until their
successors shall have been elected by such holders or until the expiration of
the default period, and (y) any vacancy in the Board of Directors may (except as
provided in paragraph (C)(ii) of this Section 3) be filled by a vote of a
majority of the remaining Directors theretofore elected by the holders of the
class of stock which elected the Director whose office shall become vacant.
References in this paragraph (C) to Directors elected by the holders of a
particular class of stock shall include Directors elected by such Directors to
fill vacancies as provided in clause (y) of the foregoing sentence.

                           (v)   Immediately upon the expiration of a default
period, (x) the right of the holders of Preferred Stock as a class to elect
Directors shall cease, (y) the term of any Directors elected by the holders of
Preferred Stock as a class shall terminate, and (z) the number of Directors
shall be such number as may be provided for in the Certificate of Incorporation
or By-laws irrespective of any increase made pursuant to the provisions of
paragraph (C)(ii) of this Section 3 (such number being subject, however, to
change thereafter in any manner provided by law or in the Certificate of
Incorporation or By-laws). Any vacancies in the Board of Directors effected by
the provisions of clauses (y) and (z) in the preceding sentence may be filled by
a majority of the remaining Directors.

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                  (D) Except as set forth herein, holders of Series A Junior
Participating Preferred Stock shall have no special voting rights and their
consent shall not be required (except to the extent they are entitled to vote
with holders of Common Stock as set forth herein) for taking any corporate
action.

                  Section 4.  Certain Restrictions.

                  (A) Whenever quarterly dividends or other dividends or
distributions payable on the Series A Junior Participating Preferred Stock as
provided in Section 2 are in arrears, thereafter and until all accrued and
unpaid dividends and distributions, whether or not declared, on shares of Series
A Junior Participating Preferred Stock outstanding shall have been paid in full,
the Corporation shall not:

                           (i)   Declare or pay dividends on, make any other
distributions on, or redeem or purchase or otherwise acquire for consideration
any shares of stock ranking junior (either as to dividends or upon liquidation,
dissolution or winding up) to the Series A Junior Participating Preferred Stock;

                           (ii)  Declare or pay dividends on or make any other
distributions on any shares of stock ranking on a parity (either as to dividends
or upon liquidation, dissolution or winding up) with the Series A Junior
Participating Preferred Stock except dividends paid ratably on the Series A
Junior Participating Preferred Stock and all such parity stock on which
dividends are payable or in arrears in proportion to the total amounts to which
the holders of all such shares are then entitled;

                           (iii) Redeem or purchase or otherwise acquire for
consideration shares of any stock ranking on a parity (either as to dividends or
upon liquidation, dissolution or winding up) with the Series A Junior
Participating Preferred Stock provided that the Corporation may at any time
redeem, purchase or otherwise acquire shares of any such parity stock in
exchange for shares of any stock of the Corporation ranking junior (either as to
dividends or upon dissolution, liquidation or winding up) to the Series A Junior
Participating Preferred Stock; or

                           (iv)  Purchase or otherwise acquire for consideration
any shares of Series A Junior Participating Preferred Stock or any shares of
stock ranking on a parity with the Series A Junior Participating Junior
Preferred Stock except in accordance with a purchase offer made in writing or by
publication (as determined by the Board of Directors) to all holders of such
shares upon such terms as the Board of Directors, after consideration of the
respective annual dividend rates and other relative rights and preferences of
the respective series and classes, shall determine in good faith will result in
fair and equitable treatment among the respective series or classes.

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                  (B) The Corporation shall not permit any subsidiary of the
Corporation to purchase or otherwise acquire for consideration any shares of
stock of the Corporation unless the Corporation could, under paragraph (A) of
this Section 4, purchase or otherwise acquire such shares at such time and in
such manner.

                  Section 5. Reacquired Shares. Any shares of Series A Junior
Participating Preferred Stock purchased or otherwise acquired by the Corporation
in any manner whatsoever shall be retired and cancelled promptly after the
acquisition thereof. All such shares shall upon their cancellation become
authorized but unissued shares of Preferred Stock and may be reissued as part of
a new series of Preferred Stock to be created by resolution or resolutions of
the Board of Directors, subject to the conditions and restrictions on issuance
set forth herein.

                  Section 6. Liquidation, Dissolution or Winding Up.

                  (A) Upon any liquidation (voluntary or otherwise), dissolution
or winding up of the Corporation, no distribution shall be made to the holders
of shares of stock ranking junior (either as to dividends or upon liquidation,
dissolution or winding up) to the Series A Junior Participating Preferred Stock
unless, prior thereto, the holders of shares of Series A Junior Participating
Preferred Stock shall have received per share, the amount of $18.00, plus an
amount equal to accrued and unpaid dividends and distributions thereon, whether
or not declared, to the date of such payment (the "Series A Liquidation
Preference"). Following the payment of the full amount of the Series A
Liquidation Preference, no additional distributions shall be made to the holders
of shares of Series A Junior Participating Preferred Stock unless, prior
thereto, the holders of shares of Common Stock shall have received an amount per
share (the "Common Adjustment") equal to the quotient obtained by dividing (i)
the Series A Liquidation Preference by (ii) 100 (as appropriately adjusted as
set forth in paragraph (C) below to reflect such events as stock splits, stock
dividends and recapitalizations with respect to the Common Stock) (such number
in clause (ii), the "Adjustment Number"). Following the payment of the full
amount of the Series A Liquidation Preference and the Common Adjustment in
respect of all outstanding shares of Series A Junior Participating Preferred
Stock and Common Stock, respectively, holders of Series A Junior Participating
Preferred Stock and holders of shares of Common Stock shall receive their
ratable and proportionate share of the remaining assets to be distributed in the
ratio of the Adjustment Number to 1 with respect to such Preferred Stock and
Common Stock, on a per share basis, respectively.

                  (B) In the event there are not sufficient assets available to
permit payment in full of the Series A Liquidation Preference and the
liquidation preferences of all other series of Preferred Stock, if any, which
rank on a parity with the Series A Junior Participating Preferred Stock, then
such remaining assets shall be distributed ratably to the holders of such parity
shares in proportion to their respective liquidation preferences.

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In the event there are not sufficient assets available to permit payment in full
of the Common Adjustment, then such remaining assets shall be distributed
ratably to the holders of Common Stock.

                  (C) In the event the Corporation shall at any time after the
Rights Declaration Date (i) declare any dividend on Common Stock payable in
shares of Common Stock, (ii) subdivide the outstanding Common Stock, or (iii)
combine the outstanding Common Stock into a smaller number of shares, then in
each case the Adjustment Number in effect immediately prior to such event shall
be adjusted by multiplying such Adjustment Number by a fraction the numerator of
which is the number of shares of Common Stock outstanding immediately after such
event and the denominator of which is the number of shares of Common Stock that
were outstanding immediately prior to such event.

                  Section 7. Consolidation, Merger, etc. If the Corporation
shall enter into any consolidation, merger, combination or other transaction in
which the shares of Common Stock are exchanged for or changed into other stock
or securities, cash and/or any other property, then in any such event the shares
of Series A Junior Participating Preferred Stock shall at the same time be
similarly exchanged or changed in an amount per share (subject to the provision
for adjustment hereinafter set forth) equal to the Adjustment Number times the
aggregate amount of stock, securities, cash and/or any other property (payable
in kind), as the case may be, into which or for which each share of Common Stock
is changed or exchanged.

                  Section 8.  No Redemption.  The shares of Series A Junior
Participating Preferred Stock shall not be redeemable.

                  Section 9. Ranking. The Series A Junior Participating
Preferred Stock shall rank junior to all other series of the Corporation's
Preferred Stock as to the payment of dividends and the distribution of assets,
unless the terms of any such series shall provide otherwise.

                  Section 10. Fractional Shares. Series A Junior Participating
Preferred Stock may be issued in fractions of a share which shall entitle the
holder, in proportion to such holder's fractional shares, to exercise voting
rights, receive dividends, participate in distributions and to have the benefit
of all other rights of holders of Series A Junior Participating Preferred Stock.

                  Section 11. Amendment. The Certificate of Incorporation of the
Corporation shall not be further amended in any manner which would materially
alter or change the powers, preferences or special rights of the Series A Junior
Participating Preferred Stock so as to affect them adversely without the
affirmative vote of the holders

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of a majority or more of the outstanding shares of Series A Junior Participating
Preferred Stock, voting separately as a class.

                  Section 12. Effective Date. This Amended Certificate of
Designation, Preferences and Rights of Series A Junior Participating Preferred
Stock of Cabot Corporation shall be effective at 5:00 P.M., Eastern Standard
Time, on November 24, 1995.

                  IN WITNESS WHEREOF, I have executed and subscribed this
Certificate and do affirm the foregoing as true under penalties of perjury this
10th day of November, 1995.

                                                     By:/s/ Kennett F. Burnes
                                                        ------------------------
                                                        Kennett F. Burnes
                                                        President

Attest:

/s/ Charles D. Gerlinger
- --------------------------

Charles D. Gerlinger
Secretary

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