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                                                                    EXHIBIT 99.6




                          REGISTRATION RIGHTS AGREEMENT


                  REGISTRATION RIGHTS AGREEMENT, dated as of July 17, 1998 (this
"Agreement"), by and between THE UNIMARK GROUP, INC., a Texas corporation (the
"Company"), and M & M Nominee L.L.C., a Delaware limited liability company (the
"Investor").

         1.       Background. The Company and the Investor have entered into a
Purchase Agreement, dated as of the date hereof (the "Purchase Agreement"). In
order to induce the Investor to enter into and consummate the transactions
contemplated by the Purchase Agreement, the Company has agreed to provide the
registration rights set forth in this Agreement. The execution and delivery of
this Registration Rights Agreement is a condition to the execution and delivery
of, and Closing under, the Purchase Agreement.

         2.       Definitions. Capitalized terms used but not defined herein 
shall have the respective meanings given to them in the Purchase Agreement. As
used herein, unless the context otherwise requires, the following terms have the
following respective meanings:

                  "Option Shares" means the shares of Common Stock or other
equity securities issued or issuable upon exercise of either the First Option or
the Second Option.

                  "Incidental Registration" is defined in Section 3.2.

                  "Participating Holders" means the holders of Registrable 
Securities participating in the particular registration.

                  "Registration Expenses" means all expenses incident to the
Company's performance of or compliance with Section 3, including, without
limitation, all registration, filing and applicable fees of the Commission,
stock exchange or NASD registration and filing fees and all listing fees and
fees with respect to the inclusion of securities in NASDAQ (as defined in
Section 3.3(j)), all fees and expenses of complying with state securities or
blue sky laws (including fees and disbursements of counsel to the underwriters
or the Participating Holders in connection with "blue sky" qualification of the
Registrable Securities and determination of their eligibility for investment
under the laws of the various jurisdictions), all word processing, duplicating
and printing expenses, all messenger and delivery expenses, the fees and
disbursements of counsel for the Company and of its independent public
accountants including the expenses of "cold comfort" letters required by or
incident to such registration, all fees and disbursements of underwriters
customarily paid by issuers or sellers of securities, all transfer taxes, and 
the
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fees and expenses of one counsel to the Participating Holders (selected by
the Requisite Percentage of Participating Holders); provided, however, that
Registration Expenses shall exclude and the Participating Holders shall pay
underwriters' fees and underwriting discounts and commissions in respect of the
Registrable Securities being registered.

                  "Registrable Securities" means (i) any Primary Shares, (ii)
any Option Shares and (iii) any shares purchased from certain executives of the
Company pursuant to the Shareholders Agreement, dated as of the date hereof, by
and among the Investor, Rafael Vaquero Bazan and Fernando Camacho Casas. As to
any particular Registrable Securities, such securities shall cease to be
Registrable Securities (a) when a registration statement with respect to the
sale of such securities shall have become effective under the Securities Act and
such securities shall have been disposed of in accordance with such registration
statement, (b) when such securities shall have been otherwise transferred, new
certificates for them not bearing a legend restricting further transfer under
the Securities Act shall have been delivered by the Company and subsequent
public distribution of them shall not require registration of them under the
Securities Act, (c) when such securities are sold pursuant to Rule 144 (or
similar rule adopted by the Commission) under the Securities Act, or (d) when
such securities cease to be outstanding.

                  "Requested Registration" is defined in Section 3.1(a).

                  "Requisite Percentage of Outstanding Holders" mean the holders
of Registrable Securities who hold 33% or more of the total Option Shares and
Primary Shares (counted as a single group) that are then outstanding (assuming
that the then exercisable portion of the First Option (if any) and the then
exercisable portion of the Second Option (if any) had been exercised for Option
Shares).

                  "Requisite Percentage of Participating Holders" means
Participating Holders of Registrable Securities who hold a majority of the total
Option Shares and Primary Shares (counted as a single group) that are then be
held by all Participating Holders (assuming that the then exercisable portion of
the First Option (if any) and the then exercisable portion of the Second Option
(if any) had been exercised for Option Shares).

         3.       Registration Under Securities Act, etc.

                  3.1      Requested Registrations.

                           (a)      Request for Registration. Subject to the 
limitations imposed by Sections 3.1(c), at any time and from time to time, one
or more holders of Registrable Securities representing the Requisite Percentage
of Outstanding Holders shall have the right to require the Company to file a
registration statement under the Securities Act 



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covering all or any part of their respective Registrable Securities, by
delivering a written request therefor to the Company specifying the number and
amount of Registrable Securities and the intended method of distribution
thereof. Any such request pursuant to this Section 3.1(a) is referred to herein
as a "Requested Registration." The Company shall give prompt written notice of
each Requested Registration to all other holders of record of Registrable
Securities, and thereupon the Company shall use its best efforts to effect the
registration under the Securities Act so as to permit promptly the sale, in
accordance with the intended method of distribution, of the Registrable
Securities which the Company has been so requested to register in the Requested
Registration and all other Registrable Securities which the Company has been
requested to register by the holders thereof by written request given to the
Company within 30 days after the giving of such written notice by the Company.

                           (b)      Registration of Other Securities. Whenever 
the Company shall effect a registration pursuant to this Section 3.1 in
connection with an underwritten offering by one or more Participating Holders of
Registrable Securities, no securities other than Registrable Securities shall be
included among the securities covered by such registration unless (i)
Participating Holders representing the Requisite Percentage of Participating
Holders shall have consented in writing to the inclusion therein of such other
securities and (ii) such inclusion shall be permitted only to the extent that it
is pursuant to and subject to the terms of the underwriting agreement or
arrangements and the inclusion of such securities will not have a material
adverse effect on the offering (including, without limitation, on the pricing of
the offering).

                           (c)      Limitations on Requested Registrations; 
Expenses. The rights of holders of Registrable Securities to request Requested
Registrations pursuant to Section 3.1(a) are subject to the following
limitations: (i) the Company shall not be obligated to effect a Requested
Registration having an aggregate anticipated offering price of less than
U.S.$2,000,000 unless such offering shall cover all remaining Registrable
Securities; (ii) the offering of Registrable Securities requested to be
registered pursuant to Section 3.1(a) shall be pursuant to a firm commitment
underwritten offering; (iii) the Company shall not be obligated to effect a
Requested Registration within six months after the effective date of any other
registration of securities (other than pursuant to a registration on Form S-8 or
any successor or similar form which is then in effect); and (iv) the Company
will pay all Registration Expenses only in connection with the first three
Requested Registrations of Registrable Securities pursuant to this Section 3.1
that have become effective under the Securities Act.

                           (d)      Registration Statement Form. Registrations 
under this Section 3.1 shall be on Form S-3 or any successor form, if permitted,
or such appropriate registration form of the Commission as shall be selected by
the Company and as shall be


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reasonably acceptable to the Requisite Percentage of Participating Holders. The
Company agrees to include in any such registration statement all information
which, in the opinion of counsel to the Participating Holders and counsel to the
Company, is required to be included.

                           (e)      Effective Registration Statement. A 
registration requested pursuant to this Section 3.1 shall not be deemed to have
been effected (including for purposes of paragraph (c) of this Section 3.1) (i)
unless a registration statement with respect thereto has become effective and
has been kept continuously effective for a period of at least 90 days (or such
shorter period which shall terminate when all the Registrable Securities covered
by such registration statement have been sold pursuant thereto), (ii) if, after
it has become effective, such registration is interfered with by any stop order,
injunction or other order or requirement of the Commission or other Governmental
Authority or court for any reason not attributable to the Participating Holders
and has not thereafter become effective, or (iii) if the conditions to closing
specified in the underwriting agreement, if any, entered into in connection with
such registration are not satisfied or waived, other than by reason of a failure
on the part of the Participating Holders.

                           (f)      Selection of Underwriters. The managing 
underwriter or underwriters of each underwritten offering of the Registrable
Securities so to be registered shall be selected by the Requisite Percentage of
Participating Holders (and shall be reasonably acceptable to the Company).

                           (g)      Cutbacks in Requested Registration. If the 
managing underwriter of any underwritten offering shall advise the Participating
Holders in such offering that the Registrable Securities covered by the
registration statement cannot be sold in such offering within a price range
acceptable to the Requisite Percentage of Participating Holders, then the
Participating Holders representing the Requisite Percentage of Participating
Holders shall have the right to notify the Company in writing that they have
determined that the registration statement be abandoned or withdrawn, in which
event the Company shall abandon or withdraw such registration statement (and, at
the option of the Requisite Percentage of Participating Holders, the
Participating Holders shall either (i) reimburse the Company for its expenses
incurred in connection with such abandoned or withdrawn registration statement
or (ii) allow the Company to count such abandoned or withdrawn registration
statement as one of the three Requested Registrations under Section 3.1(c)(iv)).
If the managing underwriter of any underwritten offering shall advise the
Company in writing (with a copy to each Participating Holder) that, in its
opinion, the number of securities requested to be included in such registration
exceeds the number which can be sold in such offering within a price range
acceptable to the Requisite Percentage of Participating Holders, the Company
will include in such 


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registration, to the extent of the number which the Company is so advised can be
sold in such offering, Registrable Securities requested to be included in such
registration, pro rata among the Participating Holders requesting such
registration in accordance with the number of Primary Shares and Option Shares
held by (or issuable to) each such Participating Holder so requested to be
registered, and any securities of the Company included in such registration
pursuant to Section 3.1(b) shall be reduced proportionately.

                           (h)      Postponement. The Company shall be entitled 
once in any six-month period to postpone for a reasonable period of time (but
not exceeding 90 days) the filing of any registration statement required to be
prepared and filed by it pursuant to this Section 3.1 if the Company determines,
in its reasonable judgment, that such registration and offering would interfere
with any financing, corporate reorganization or other material transaction or
development involving the Company or any subsidiary or would require premature
disclosure thereof, and promptly gives the holders of Registrable Securities
requesting registration thereof pursuant to this Section 3.1 written notice of
such determination, containing a statement of the reasons for such postponement
and an approximation of the anticipated delay. If the Company shall so postpone
the filing of a registration statement, the Participating Holders representing
the Requisite Percentage of Participating Holders shall have the right to
withdraw the request for registration by giving written notice to the Company
within 20 days after receipt of the notice of postponement and, in the event of
such withdrawal, such request shall not be counted toward the number of
Requested Registrations (including for purposes of paragraph (c) of this Section
3.1).

                  3.2      Incidental Registration.

                           (a)      Incidental Registration. If, at any time, 
the Company proposes or is required to register any of its equity securities or
securities convertible into or exchangeable for equity securities under the
Securities Act (other than pursuant to registrations on such form or similar
form(s) solely for registration of securities in connection with an employee
benefit plan or dividend reinvestment plan) (an "Incidental Registration"), the
Company will give prompt written notice to all holders of record of Registrable
Securities of its intention to so register its securities and of such holders'
rights under this Section 3.2. Upon the written request of any holder of
Registrable Securities made within 20 days following the receipt of any such
written notice (which request shall specify the maximum number of Registrable
Securities intended to be disposed of by such holder and the intended method of
distribution thereof), the Company will use its best efforts to effect the
registration under the Securities Act of all Registrable Securities which the
Company has been so requested to register by the holders thereof together with
any other securities the Company is obligated to register pursuant to incidental
registration rights of other security holders of the Company. No registration


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effected under this Section 3.2 shall relieve the Company of its obligation to
effect any Requested Registration under Section 3.1.

                           (b)      Abandonment or Delay. If, at any time after 
the Company has giving written notice of its intention to register any
securities and prior to the effective date of the registration statement filed
in connection with such registration, the Company shall determine not to
register or to delay registration of such securities, the Company may, at its
election, give written notice of such determination and its reasons therefor to
all holders of record of Registrable Securities and (i) in the case of a
determination not to register, shall be relieved of its obligation to register
any Registrable Securities in connection with such registration (but not from
any obligation of the Company to pay the Registration Expenses in connection
therewith) , without prejudice, however, to the rights of any holder or holders
of Registrable Securities entitled to do so to request that such registration be
effected as a registration under Section 3.1, and (ii) in the case of a
determination to delay registering, shall be permitted to delay registering any
Registrable Securities for the same period as the delay in registering such
other securities.

                           (c)      Holder's Right to Withdraw. Each holder of
Registrable Securities shall have the right to withdraw its request for
inclusion of its Registrable Securities in any registration statement pursuant
to this Section 3.2 at any time by giving written notice to the Company of its
request to withdraw.

                           (d)      Unlimited Number of Registrations; Expenses.
There is no limitation on the number of Incidental Registrations which the
Company is obligated to effect pursuant to this Section 3.2. The Company will
pay all Registration Expenses in connection with any registration of Registrable
Securities requested pursuant to this Section 3.2.

                           (e)      Underwriters' Cutback in Incidental 
Registrations. If the managing underwriter of any underwritten offering shall
inform the Company by letter of its belief that the number of Registrable
Securities requested to be included in such registration would materially
adversely affect such offering, then the Company will include in such
registration, first, the securities proposed by the Company to be sold for its
own account and, second, the Registrable Securities and all other securities of
the Company to be included in such registration to the extent of the number and
type which the Company is so advised can be sold in (or during the time of) such
offering, pro rata among the Participating Holders and such other holders
requesting such registration in accordance with the number of Primary Shares and
Option Shares held by (or issuable to) each Participating Holder and each such
other holder so requested to be registered.



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                           (f)     Plan of Distribution. Any participation by 
holders of Registrable Securities in a registration by the Company shall be in
accordance with the Company's plan of distribution.

                  3.3      Registration Procedures. If and whenever the Company 
is required to use its best efforts to effect the registration of any
Registrable Securities under the Securities Act as provided in Sections 3.1 or
3.2 hereof, the Company will as expeditiously as possible:

                           (a)     prepare and file with the Commission as soon 
                  as practicable the requisite registration statement to effect
                  such registration (and shall include all financial statements
                  required by the Commission to be filed therewith) and
                  thereafter use its best efforts to cause such registration
                  statement to become effective; provided, however, that before
                  filing such registration statement (including all exhibits) or
                  any amendment or supplement thereto or comparable statements
                  under securities or blue sky laws of any jurisdiction, the
                  Company shall furnish such documents to the Participating
                  Holders, their counsel, and each underwriter, if any,
                  participating in the offering of the Registrable Securities
                  and its counsel; and provided, further, however, that the
                  Company may discontinue any registration of its securities
                  which are not Registrable Securities at any time prior to the
                  effective date of the registration statement relating thereto;

                           (b)     notify each Participating Holder of the
                  Commission's requests for amending or supplementing the
                  registration statement and the prospectus, and prepare and
                  file with the Commission such amendments and supplements to
                  such registration statement and the prospectus used in
                  connection therewith as may be necessary to keep such
                  registration statement effective and to comply with the
                  provisions of the Securities Act with respect to the
                  disposition of all Registrable Securities covered by such
                  registration statement for such period as shall be required
                  for the disposition of all of such Registrable Securities,
                  provided, that such period need not exceed 90 days;

                           (c)     furnish, without charge, to each
                  Participating Holder such number of conformed copies of such
                  registration statement and of each such amendment and
                  supplement thereto (in each case including all exhibits), such
                  number of copies of the prospectus contained in such
                  registration statement (including each preliminary prospectus
                  and any summary prospectus) and any other prospectus filed
                  under Rule 424 under the Securities Act, in conformity with
                  the requirements of the Securities Act, 



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                  and such other documents, as such Participating Holder may
                  reasonably request;

                           (d)     use its best efforts (i) to register or
                  qualify all Registrable Securities and other securities
                  covered by such registration statement under such securities
                  or blue sky laws of such States of the United States of
                  America where an exemption is not available and as the
                  Participating Holders shall reasonably request, (ii) to keep
                  such registration or qualification in effect for so long as
                  such registration statement remains in effect, and (iii) to
                  take any other action which may be reasonably necessary or
                  advisable to enable such Participating Holders to consummate
                  the disposition in such jurisdictions of the securities to be
                  sold by such Participating Holders, except that the Company
                  shall not for any such purpose be required to qualify
                  generally to do business as a foreign corporation in any
                  jurisdiction wherein it would not but for the requirements of
                  this subsection (d) be obligated to be so qualified or to
                  consent to general service of process in any such
                  jurisdiction;

                           (e)     use its best efforts to cause all Registrable
                  Securities covered by such registration statement to be
                  registered with or approved by such other federal or state or
                  foreign governmental agencies or authorities as may be
                  necessary in the opinion of counsel to the Company and counsel
                  to the Participating Holders to consummate the disposition of
                  such Registrable Securities;

                           (f)     furnish to each Participating Holder and each
                  underwriter, if any, participating in the offering of the
                  securities covered by such registration statement, a signed
                  counterpart of

                                   (i)     an opinion of outside counsel (or 
                           inside counsel if satisfactory to each underwriter)
                           for the Company, and

                                   (ii)    a "comfort" letter signed by the
                           independent public accountants who have certified the
                           Company's financial statements included or
                           incorporated by reference in such registration
                           statement,

                  covering substantially the same matters with respect to such
                  registration statement (and the prospectus included therein)
                  and, in the case of the accountants' comfort letter, with
                  respect to events subsequent to the date of such financial
                  statements, as are customarily covered in opinions of issuer's
                  counsel and in accountants' comfort letters delivered to the
                  underwriters in underwritten public offerings of securities
                  (and dated the dates such 


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                  opinions and comfort letters are customarily dated) and, in
                  the case of the legal opinion, such other legal matters, and,
                  in the case of the accountants' comfort letter, such other
                  financial matters, as the Requisite Percentage of
                  Participating Holders, or the underwriters, may reasonably
                  request;

                           (g)     promptly notify each Participating Holder and
                  each managing underwriter, if any, participating in the
                  offering of the securities covered by such registration
                  statement (i) when such registration statement, any
                  pre-effective amendment, the prospectus or any prospectus
                  supplement related thereto or post-effective amendment to such
                  registration statement has been filed, and, with respect to
                  such registration statement or any post-effective amendment,
                  when the same has become effective; (ii) of any request by the
                  Commission for amendments or supplements to such registration
                  statement or the prospectus related thereto or for additional
                  information; (iii) of the issuance by the Commission of any
                  stop order suspending the effectiveness of such registration
                  statement or the initiation of any proceedings for that
                  purpose; (iv) of the receipt by the Company of any
                  notification with respect to the suspension of the
                  qualification of any of the Registrable Securities for sale
                  under the securities or blue sky laws of any jurisdiction or
                  the initiation of any proceeding for such purpose; (v) at any
                  time when a prospectus relating thereto is required to be
                  delivered under the Securities Act, upon discovery that, or
                  upon the happening of any event as a result of which, the
                  prospectus included in such registration statement, as then in
                  effect, includes an untrue statement of a material fact or
                  omits to state any material fact required to be stated therein
                  or necessary to make the statements therein not misleading, in
                  the light of the circumstances under which they were made, and
                  in the case of this clause (v), at the request of any
                  Participating Holder, promptly prepare and furnish to it and
                  each managing underwriter, if any, participating in the
                  offering of the Registrable Securities a reasonable number of
                  copies of a supplement to or an amendment of such prospectus
                  as may be necessary so that, as thereafter delivered to the
                  purchasers of such securities, such prospectus shall not
                  include an untrue statement of a material fact or omit to
                  state a material fact required to be stated therein or
                  necessary to make the statements therein not misleading in the
                  light of the circumstances under which they were made; and
                  (vi) at any time when the representations and warranties of
                  the Company contemplated by Section 3.4(a) hereof cease to be
                  true and correct;

                           (h)     otherwise comply with all applicable rules 
                  and regulations of the Commission, and make available to its
                  security holders, as soon as reasonably practicable, an
                  earnings statement covering the period of at least 


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                  twelve months beginning with the first full calendar month
                  after the effective date of such registration statement, which
                  earnings statement shall satisfy the provisions of Section
                  11(a) of the Securities Act and Rule 158 promulgated
                  thereunder, and promptly furnish to each such Participating
                  Holder a copy of any amendment or supplement to such
                  registration statement or prospectus;

                           (i)     provide and cause to be maintained a transfer
                  agent and registrar (which, in each case, may be the Company)
                  for all Registrable Securities covered by such registration
                  statement from and after a date not later than the effective
                  date of such registration;

                           (j)     use its best efforts to cause all Registrable
                  Securities covered by such registration statement to be listed
                  on a national securities exchange or to secure designation of
                  all such Registrable Securities as a National Association of
                  Securities Dealers, Inc. Automated Quotation System ("NASDAQ")
                  "national market system security" within the meaning of Rule
                  11Aa2-1 of the Commission, in each case to the extent the
                  shares of the Company's Common Stock are so listed or
                  designated;

                           (k)     deliver promptly to counsel to the
                  Participating Holders and each underwriter, if any,
                  participating in the offering of the Registrable Securities,
                  copies of all correspondence between the Commission and the
                  Company, its counsel or auditors and all memoranda relating to
                  discussions with the Commission or its staff with respect to
                  such registration statement;

                           (1)     make every reasonable effort to obtain the 
                  withdrawal of any order suspending the effectiveness of the
                  registration statement;

                           (m)      provide a CUSIP number for all Registrable 
                  Securities, no later than the effective date of the
                  registration statement; and

                           (n)     make available its employees and personnel
                  and otherwise provide reasonable assistance to the
                  underwriters (taking into account the needs of the Company's
                  businesses) in their marketing of Registrable Securities.

The Company may require each Participating Holder as to the Registrable
Securities of whom any registration is being effected to furnish the Company
such information regarding such holder and the distribution of such securities
as the Company may from time to time reasonably request in writing.


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                  Each holder of Registrable Securities agrees that upon receipt
of any notice from the Company of the happening of any event of the kind
described in subsection (g) (iii) or (v) of this Section 3.3, the Participating
Holder will forthwith discontinue such holder's disposition of Registrable
Securities pursuant to the registration statement relating to such Registrable
Securities until, in the case of subsection (g)(iii) of this Section 3.3, such
stop order is removed or proceedings therefor terminated, and, in the case of
subsection (g)(v) of this Section 3.3, such holder's receipt of the copies of
the supplemented or amended prospectus contemplated by subsection (g)(v) of this
Section 3.3 and, if so directed by the Company, will deliver to the Company (at
the Company's expense) all copies, other than permanent file copies, then in
such holder's possession, of the prospectus relating to such Registrable
Securities current at the time of receipt of such notice.

                  3.4      Underwritten Offerings.

                           (a)      Requested Underwritten Offerings. If 
requested by the underwriters for any underwritten offering by Participating
Holders pursuant to a registration requested under Section 3.1, the Company will
use its best efforts to enter into an underwriting agreement with such
underwriters for such offering, such agreement to be reasonably satisfactory in
substance and form to the Company, each such holder and the underwriters and to
contain such representations and warranties by the Company and such other terms
as are generally prevailing in agreements of that type, including, without
limitation, indemnities to the effect and to the extent provided in Section 3.6
hereof. The Participating Holders will cooperate with the Company in the
negotiation of the underwriting agreement and will give consideration to the
reasonable suggestions of the Company regarding the form thereof. The
Participating Holders shall be parties to such underwriting agreement and may,
at their option, require that any or all of the representations and warranties
by, and the other agreements on the part of, the Company to and for the benefit
of such underwriters shall also be made to and for the benefit of the
Participating Holders and that any or all of the conditions precedent to the
obligations of such underwriters under such underwriting agreement be conditions
precedent to the obligations of the Participating Holders. No Participating
Holder shall be required to make any representations or warranties to or
agreements with the Company or the underwriters other than representations,
warranties or agreements regarding such holder, such holder's ownership of and
title to the Registrable Securities, such holder's intended method of
distribution and any other representations required by law, and any liability of
the Participating Holder to any underwriter or other person under such
underwriting agreement shall be limited to liability arising from misstatements
in or omissions from its representations and warranties and shall be limited to
an amount equal to the net proceeds that the Participating Holder derives from
such registration.


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                           (b)      Incidental Underwritten Offerings. If the 
Company proposes to register any of its securities under the Securities Act as
contemplated by Section 3.2 hereof and such securities are to be distributed by
or through one or more underwriters, the Company will, if requested by any
Participating Holder, use its best efforts to arrange for such underwriters to
include all the Registrable Securities to be offered and sold by such
Participating Holder among the securities of the Company to be distributed by
such underwriters. The Participating Holders shall be parties to the
underwriting agreement between the Company and such underwriters and may, at
their option, require that any or all of the representations and warranties by,
and the other agreements on the part of, the Company to and for the benefit of
such underwriters shall also be made to and for the benefit of such
Participating Holders and that any or all of the conditions precedent to the
obligations of such underwriters under such underwriting agreement be conditions
precedent to the obligations of such Participating Holders. No Participating
Holder shall be required to make any representations or warranties to or
agreements with the Company or the underwriters other than representations,
warranties or agreements regarding such holder, such holder's ownership of and
title to the Registrable Securities, such holder's intended method of
distribution and any other representations required by law, and any liability of
the Participating Holder to any underwriter or other person under such
underwriting agreement shall be limited to liability arising from misstatements
in or omissions from its representations and warranties and shall be limited to
an amount equal to the net proceeds that the Participating Holder derives from
such registration.

                  3.5      Preparation; Reasonable Investigation. In connection
with the preparation and filing of each registration statement under the
Securities Act pursuant to this Agreement, the Company will give the
Participating Holders, their underwriters, if any, and their respective counsel
and accountants the opportunity to participate in the preparation of such
registration statement, each prospectus included therein or filed with the
Commission, and, to the extent practicable, each amendment thereof or supplement
thereto, and give each of them such access to its books and records and such
opportunities to discuss the business of the Company with its officers and
employees and the independent public accountants who have certified its
financial statements as shall be necessary, in the opinion of such holders' and
such underwriters' respective counsel, to conduct a reasonable investigation
within the meaning of the Securities Act.

                  3.6      Indemnification.

                           (a)      Indemnification by the Company. In the event
of any registration of any securities of the Company under the Securities Act,
the Company will, and hereby does, indemnify and hold harmless, to the fullest
extent permitting by law, each Participating Holder, its directors, officers,
partners, agents and affiliates or general and limited partners (and the
directors, officers, employees, stockholders and affiliates



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<PAGE>   13

thereof), and each other Person who participates as an underwriter in the
offering or sale of such securities and each other Person, if any, who
controls such Participating Holder or any such underwriter within the meaning
of the Securities Act, against any losses, claims, damages, or liabilities,
joint or several (or actions or proceedings, whether commenced or threatened)
to which such Participating Holder or any such director, officer, partner,
agent or affiliate or underwriter or controlling person may become subject
under the Securities Act or otherwise, insofar as such losses, claims,
damages or liabilities, joint or several (or actions or proceedings, whether
commenced or threatened, in respect thereof) arise out of or are based upon any
untrue statement or alleged untrue statement of any material fact contained in
any registration statement under which such securities were registered under the
Securities Act, any preliminary prospectus, final prospectus or summary
prospectus contained therein, or any amendment or supplement thereto, together
with the documents incorporated by reference therein, or any omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements therein in light of the circumstances in which
they were made not misleading, and the Company will reimburse such Participating
Holder and each such director, officer, partner, agent or affiliate, or general
or limited partner, underwriter and controlling Person for any legal or any
other expenses reasonably incurred by them in connection with investigating or
defending any such loss, claim, liability, action or proceeding; provided, that
the Company shall not be liable in any such case to the extent that any such
loss, claim, damage, liability (or action or proceeding in respect thereof) or
expense arises out of or is based upon an untrue statement or alleged untrue
statement or omission or alleged omission made in such registration statement,
any such preliminary prospectus, final prospectus, summary prospectus, amendment
or supplement in reliance upon and in conformity with written information
furnished to the Company through an instrument duly executed by or on behalf of
such Participating Holder or underwriter, as the case may be, specifically
stating that it is for use in the preparation thereof; and provided, further,
that the Company shall not be liable to any Person who participates as an
underwriter in the offering or sale of Registrable Securities or any other
Person, if any, who controls such underwriter within the meaning of the
Securities Act, in any such case to the extent that any such loss, claim,
damage, liability (or action or proceeding in respect thereof) or expense arises
out of such Person's failure to send or give a copy of the final prospectus, as
the same may be then supplemented or amended, to the Person asserting an untrue
statement or alleged untrue statement or omission or alleged omission at or
prior to the written confirmation of the sale of Registrable Securities to such
Person if such statement or omission was corrected in such final prospectus.
Such indemnity shall remain in full force regardless of any investigation made
by or on behalf of such Participating Holder or any such director, officer,
partner, agent or affiliate or controlling Person and shall survive the transfer
of such securities by such Participating Holder.


                                      -13-
<PAGE>   14

                           (b)      Indemnification by the Participating 
Holders. As a condition to including any Registrable Securities in any
registration statement, the Company shall have received an undertaking
satisfactory to it from the Participating Holders to indemnify and hold harmless
(in the same manner and to the same extent as set forth in subsection (a) of
this Section 3.6) the Company, each director and officer of the Company, and
each other Person, if any, who controls the Company within the meaning of the
Securities Act, with respect to any statement or alleged statement in or
omission or alleged omission from such registration statement, any preliminary
prospectus, final prospectus or summary prospectus contained therein, or any
amendment or supplement thereto, but only if such statement or alleged statement
or omission or alleged omission was made in reliance upon and in conformity with
written information furnished to the Company through an instrument duly executed
by such Participating Holder specifically stating that it is for use in the
preparation of such registration statement, preliminary prospectus, final
prospectus, summary prospectus, amendment or supplement; provided, however, that
the liability of such indemnifying party under this Section 3.6(b) shall be
limited to the amount of net proceeds received by such indemnifying party in the
offering giving rise to such liability. Such indemnity shall remain in full
force and effect, regardless of any investigation made by or on behalf of the
Company or any such director, officer or controlling person and shall survive
the transfer of such securities by the Participating Holder.

                           (c)      Notices of Claims, etc.  Promptly after 
receipt by an indemnified party of notice of the commencement of any action or
proceeding involving a claim referred to in the preceding subsections of this
Section 3.6, such indemnified party will, if a claim in respect thereof is to be
made against an indemnifying party, give written notice to the latter of the
commencement of such action or proceeding; provided, however, that the failure
of any indemnified party to give notice as provided herein shall not relieve the
indemnifying party of its obligations under the preceding subsections of this
Section 3.6, except to the extent that the indemnifying party is materially
prejudiced by such failure to give notice, and shall not relieve the
indemnifying party from any liability which it may have to the indemnified party
otherwise than under this Section 3.6. In case any such action or proceeding is
brought against an indemnified party, the indemnifying party shall be entitled
to participate therein and, unless in the opinion of outside counsel to the
indemnified party a conflict of interest between such indemnified and
indemnifying parties may exist in respect of such claim, to assume the defense
thereof, jointly with any other indemnifying party similarly notified to the
extent that it may wish, with counsel reasonably satisfactory to such
indemnified party; provided, however, that if the defendants in any such action
or proceeding include both the indemnified party and the indemnifying party and
if in the opinion of outside counsel to the indemnified party there may be legal
defenses available to such indemnified party 


                                      -14-
<PAGE>   15

and/or other indemnified parties which are different from or in addition to
those available to the indemnifying party, the indemnified party or parties
shall have the right to select separate counsel to defend such action or
proceeding on behalf of such indemnified party or parties, provided, further,
that the indemnifying party shall be obligated to pay for only one counsel for
all indemnified parties. After notice from the indemnifying party to such
indemnified party of its election so to assume the defense thereof and approval
by the indemnified party of such counsel, the indemnifying party shall not be
liable to such indemnified party for any legal expenses subsequently incurred by
the latter in connection with the defense thereof other than reasonable costs of
investigation (unless the first proviso in the preceding sentence shall be
applicable). No indemnifying party shall be liable for any settlement of any
action or proceeding effected without its written consent. No indemnifying party
shall, without the consent of the indemnified party, consent to entry of any
judgment or enter into any settlement which does not include as an unconditional
term thereof the giving by the claimant or plaintiff to such indemnified party
of a release from all liability in respect to such claim or litigation.

                           (d)      Contribution. If the indemnification 
provided for in this Section 3.6 shall for any reason be held by a court to be
unavailable to an indemnified party under subsection (a) or (b) hereof in
respect of any loss, claim, damage or liability, or any action in respect
thereof, then, in lieu of the amount paid or payable under subsection (a) or (b)
hereof, the indemnified party and the indemnifying party under subsection (a) or
(b) hereof shall contribute to the aggregate losses, claims, damages and
liabilities (including legal or other expenses reasonably incurred in connection
with investigating the same), (i) in such proportion as is appropriate to
reflect the relative fault of the Company and the Participating Holders which
resulted in such loss, claim, damage or liability, or action in respect thereof,
with respect to the statements or omissions which resulted in such loss, claim,
damage or liability, or action in respect thereof, as well as any other relevant
equitable considerations or (ii) if the allocation provided by clause (i) above
is not permitted by applicable law, in such proportion as shall be appropriate
to reflect not only the relative fault but also the relative benefits received
by the Company and the Participating Holders from the offering of the securities
covered by such registration statement as well as any other relevant equitable
considerations. The parties hereto agree that it would not be just and equitable
if contributions pursuant to this Section 3.6(d) were to be determined by pro
rata allocation or by any other method of allocation which does not take account
of the equitable considerations referred to above. No Person guilty of
fraudulent misrepresentation (within the meaning of Section 11(f) of the
Securities Act) shall be entitled to contribution from any Person who was not
guilty of such fraudulent misrepresentation. The Participating Holders'
obligations to contribute as provided in this subsection (d) are several and not
joint in proportion to the relative value of their respective Registrable
Securities covered by such registration statement. In 


                                      -15-
<PAGE>   16

addition, no Person shall be obligated to contribute hereunder any amounts in
payment for any settlement of any action or claim effected without such Person's
consent, which consent shall not be unreasonably withheld. Notwithstanding
anything in this subsection (d) to the contrary, no indemnifying party (other
than the Company) shall be required to contribute any amount in excess of the
net proceeds received by such party from the sale of the Registrable Securities
in the offering to which the losses, claims, damages or liabilities of the
indemnified parties relate.

                           (e)      Other Indemnification. Indemnification and 
contribution similar to that specified in the preceding subsections of this
Section 3.6 (with appropriate modifications) shall be given by the Company and
each Participating Holder with respect to any required registration or other
qualification of securities under any federal or state law or regulation of any
governmental authority other than the Securities Act. The indemnification
agreements contained in this Section 3.6 shall be in addition to any other
rights to indemnification or contribution which any indemnified party may have
pursuant to law or contract and shall remain operative and in full force and
effect regardless of any investigation made by or on behalf of any indemnified
party and shall survive the transfer of any of the Registrable Securities by any
of the Participating Holders.

                           (f)      Indemnification Payments. The 
indemnification and contribution required by this Section 3.6 shall be made by
periodic payments of the amount thereof during the course of the investigation
or defense, as and when bills are received or expense, loss, damage or liability
is incurred.

                  3.7      Certain Rights of the Investor If Named in a 
Registration Statement. If any statement contained in a registration statement
under the Securities Act or in any filing under the state securities laws of any
jurisdiction refers to the Investor by name or otherwise as the holder of any
securities of the Company, then the Investor shall have the right to require (i)
the insertion therein of language, in form and substance satisfactory to the
Investor, to the effect that the holding by the Investor of such securities does
not necessarily make the Investor a "controlling person" of the Company within
the meaning of the Securities Act and is not to be construed as a recommendation
by the Investor of the investment quality of the Company's debt or equity
securities covered thereby and that such holding does not imply that the
Investor will assist in meeting any future financial requirements of the Company
or (ii) in the event that such reference to the Investor by name or otherwise is
not, in the reasonable judgment of the Investor as advised by its counsel,
required by the Securities Act or any of the rules and regulations promulgated
thereunder, or any state securities laws of any jurisdiction, the deletion of
the reference to such Investor.



                                      -16-


<PAGE>   17

                  3.8      Unlegended Certificates. In connection with the
offering of any Registrable Securities registered pursuant to this Article 3,
the Company shall (i) facilitate the timely preparation and delivery to
Participating Holders and the underwriters, if any, participating in such
offering, of unlegended certificates representing ownership of such Registrable
Securities being sold in such denominations and registered in such names as
requested by such Participating Holders or such underwriters and (ii) instruct
any transfer agent and registrar of such Registrable Securities to release any
stop transfer orders with respect to any such Registrable Securities.

                  3.9      Limitation on Sale or Distribution of Other
Securities. The Company hereby agrees that, if it shall previously have received
a request for registration pursuant to Section 3.1 or 3.2 hereof, and if such
previous registration shall not have been withdrawn or abandoned, (i) the
Company shall not effect any public or private offer, sale or other distribution
of its securities or effect any registration of any of its equity securities
under the Securities Act (subject to the provisions of Section 3.2 hereof)
(other than a registration on Form S-8 or any successor or similar form which is
then in effect), whether or not for sale for its own account, until a period of
90 days (or such shorter period as the Requisite Majority of Participating
Holders shall agree) shall have elapsed from the effective date of such previous
registration (and the Company shall so provide in any registration rights
agreements hereafter entered into with respect to any of its securities); and
(ii) the Company shall use its best efforts to cause each holder of its equity
securities purchased from the Company at any time after the date of this
Agreement other than in a public offering to agree not to effect any public sale
or distribution of any such securities during such period, including a sale
pursuant to Rule 144 under the Securities Act.

                  3.10     No Required Sale. Nothing in this Agreement shall be
deemed to create an independent obligation on the part of any Participating
Holder to sell any Registrable Securities pursuant to any effective registration
statement.

         4.       Rule 144. The Company shall take all actions reasonably
necessary to enable holders of Registrable Securities to sell such securities
without registration under the Securities Act within the limitation of the
exemptions provided by (a) Rule 144, or (b) any similar rule or regulation
hereafter adopted by the Commission including, without limiting the generality
of the foregoing, filing on a timely basis all reports required to be filed by
the Exchange Act. Upon the request of any holder of Registrable Securities, the
Company will deliver to such holder a written statement as to whether it has
complied with such requirements.

         5.       Amendments and Waivers. This Agreement may be amended with the
consent of (i) the Company and (ii) the holders of at least 51% of the
outstanding Primary 


                                      -17-
<PAGE>   18


Shares and Option Shares, as a group (assuming that the exercisable portion (if
any) of the First Option and the exercisable portion (if any) of the Second
Option are converted into Option Shares but excluding any Primary Shares or
Option Shares that are no longer Registerable Securities). The Company may take
any action herein prohibited, or omit to perform any act herein required to be
performed by it, in each case only if the Company shall have obtained the
written consent to such action or omission to act, of holders of at least 51% of
the outstanding Primary Shares and Option Shares, as a group (assuming that the
exercisable portion (if any) of the First Option and the exercisable portion (if
any) of the Second Option are converted into Option Shares but excluding any
Primary Shares or Option Shares that are no longer Registerable Securities).
Each holder of any Registrable Securities at the time or thereafter outstanding
shall be bound by any consent authorized by this Section 5, whether or not such
Registrable Securities shall have been marked to indicate such consent.

         6.       Nominees for Beneficial Owners. In the event that any
Registrable Securities are held by a nominee for the beneficial owner thereof,
the beneficial owner thereof may, at its election in writing delivered to the
Company (accompanied by a written acknowledgment of, and consent to, such
election by such nominee), be treated as the holder of such Registrable
Securities for purposes of any request or other action by any holder or holders
of Registrable Securities pursuant to this Agreement or any determination of any
number or percentage of shares of Registrable Securities held by any holder or
holders of Registrable Securities contemplated by this Agreement. If the
beneficial owner of any Registrable Securities so elects to be treated as the
holder of such Registrable Securities, the Company may require assurances
reasonably satisfactory to it of such owner's beneficial ownership of such
Registrable Securities.

         7.       Notices. All communications provided for hereunder shall be
personally delivered or sent by telecopier (and confirmed by telephone) or by a
reputable overnight courier, and shall be addressed as follows:

                  (a)    if to the Investor, addressed to it in the manner set
forth in the Purchase Agreement, or at such other address as it shall have
furnished to the Company in writing;

                  (b)    if to any other holder of Registrable Securities, at
the address that such holder shall have furnished to the Company in writing, or,
until any such other holder so furnishes to the Company an address, then to and
at the address of the last holder of such Registrable Securities who has
furnished an address to the Company; or



                                      -18-

<PAGE>   19

                  (c)    if to the Company, addressed to it in the manner set
forth in the Purchase Agreement, or at such other address as the Company shall
have furnished to each holder of Registrable Securities at the time outstanding.

         8.       Assignment. This Agreement shall be binding upon and inure to
the benefit of and be enforceable by the parties hereto and their respective
successors and permitted assigns. This Agreement may not be assigned by the
Company. This Agreement and/or the registration and other rights contained
herein (including these assignment rights) may be assigned by the Investor to
any one or more transferees or distributees of all or part of such Investor's
Registrable Securities. A holder of Registrable Securities shall be permitted,
in connection with a transfer or disposition of Registrable Securities, to
impose conditions or constraints on the ability of the transferee, as a holder
of Registrable Securities, to request a registration pursuant to Section 3.1 and
shall provide the Company with copies of such conditions or constraints and the
identity of such transferees. Notwithstanding the foregoing, this Agreement
and/or the registration and other rights contained herein may not be assigned to
a transferee or distributee who, immediately following such transfer or
distribution, owns less than one percent of the Company's outstanding Common
Stock.

         9.      Remedies. Each holder of Registrable Securities, in addition to
being entitled to exercise all rights provided herein or granted by law,
including recovery of damages, will be entitled to specific performance of its
rights under this Agreement. The Company agrees that monetary damages would not
be adequate compensation for any loss incurred by reason of a breach by it of
the provisions of this Agreement and hereby agrees to waive the defense in any
action for specific performance that a remedy at law would be adequate. In any
action or proceeding brought to enforce any provision of this Agreement
(including the indemnification provisions thereof), the successful party shall
be entitled to recover reasonable attorneys' fees in addition to its costs and
expenses and any other available remedy.

         10.     No Inconsistent Agreements. The Company will not, on or after
the date of this Agreement, enter into any agreement with respect to its
securities which is inconsistent with the rights granted to the holders of
Registrable Securities in this Agreement or otherwise conflicts with the
provisions hereof. The Company has not previously entered into any agreement
with respect to its securities granting any registration rights to any Person
other than the registration rights granted pursuant to this Agreement. The
rights granted to the holders of Registrable Securities hereunder do not in any
way conflict with and are not inconsistent with any other agreements to which
the Company is a party or by which it is bound. The Company further agrees that
if any other registration rights agreement entered into after the date of this
Agreement with respect to any of its securities contains terms which are more
favorable to, or less 


                                      -19-
<PAGE>   20

restrictive on, the other party thereto than the terms and conditions contained
in this Agreement are (insofar as they are applicable) to the Investor, then the
terms and conditions of this Agreement shall immediately be deemed to have been
amended without further action by the Company or any of the holders of
Registrable Securities so that such holders shall be entitled to the benefit of
any such more favorable or less restrictive terms or conditions.

         11.      Descriptive Headings. The descriptive headings of the several
sections and paragraphs of this Agreement are inserted for reference only and
shall not limit or otherwise affect the meaning hereof.

         12.      Governing Law; Submission to Jurisdiction; Waiver of Jury
Trial. This Agreement shall be construed and enforced in accordance with, and
the rights of the parties shall be governed by, the laws of the State of
Delaware, without regard to the conflicts of laws principles thereof. Each of
the parties hereto hereby irrevocably and unconditionally consents to submit to
the exclusive jurisdiction of the courts of the State of Delaware and the United
States of America located in Wilmington, Delaware for any action or proceeding
arising out of or relating to this Agreement and the transactions contemplated
hereby (and agrees not to commence any action or proceeding relating thereto
except in such courts). Each of the parties hereto hereby irrevocably and
unconditionally waives any objection to the laying of venue of any action or
proceeding arising out of this Agreement or the transactions contemplated hereby
in the courts of the State of Delaware or the United States of America located
in Wilmington, Delaware, and hereby further irrevocably and unconditionally
waives and agrees not to plead or claim in any such court that any such action
or proceeding brought in any such court has been brought in an inconvenient
forum. The Company hereby waives any right it may have to a trial by jury in
respect of any action, proceeding or litigation directly or indirectly arising
out of, under or in connection with, this Agreement.

         13.      Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be deemed an original, but all such
counterparts shall together constitute one and the same instrument.


                                      -20-
<PAGE>   21

        IN WITNESS WHEREOF, the parties have caused this Agreement to be
executed and delivered by their respective officers thereunto duly authorized as
of the date first above written.

                             THE UNIMARK GROUP, INC.


                             By: /s/ Rafael Vaquero Bazan
                                 ------------------------
                                 Name:      Rafael Vaquero Bazan
                                 Title:     President, Chief Executive Officer 
                                            and Chief Operating Officer





                             M & M NOMINEE L.L.C.


                             By: /s/ Peter Streinger
                                 -------------------
                                 Name:      Peter Streinger
                                 Title:     Manager