STOCK PURCHASE, DEBT ACKNOWLEDGMENT, MORTGAGE, AND TERMINATION OF OBLIGATIONS AGREEMENT (THE "AGREEMENT") ENTERED INTO

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Exhibit 10.66

(English Translation of Original Document)

STOCK PURCHASE, DEBT ACKNOWLEDGMENT, MORTGAGE, AND TERMINATION OF OBLIGATIONS

AGREEMENT (THE "AGREEMENT") ENTERED INTO BY:

(i) NATIONAL FINANCIERA, S.N.C., IN ITS CAPACITY AS FINANCIAL TRUST INSTITUTION

CAPITALIZATION AND INVESTMENT FUND FOR THE RURAL SECTOR ("FOCIR"), as Seller,

represented herein by Francisco Javier Delgado Mendoza;

(ii) The mercantile company organized and existing under the laws of the United

Mexican States "SIERRA RANCHOS, S.A. DE C.V." ("PURCHASER"); represented herein

by Mr. Jakes Jordaan, in its capacity as Sole Administrator.

(iii) The company "THE UNIMARK GROUP, INC." organized under the laws of the

State of Texas of the United States of America ("UNIMARK"); represented herein

by Mr. Jakes Jordan, as legal representative.

(iv) The mercantile company organized and existing under the laws of the United

Mexican States "GRUPO INDUSTRIAL SANTA ENGRACIA, S.A. DE C.V." ("GISE" or the

"JOINT OBLIGOR"); represented herein by Mr. Jakes Jordaan, as legal

representative.

Pursuant to the following Recitals, Representations, and Clauses:

R E C I T A L S

1. On February 21, 2000, UNIMARK, the company GMARTINEZ, S.A. DE C.V. ("GM") and

JOSE MARTINEZ BROHEZ ("JMB"), collectively, the "Private Shareholders", entered

into, along with FOCIR, a Management Partnership Agreement (Convenio de

Asociacion Empresarial) (hereinafter "CAE"), through which FOCIR and the Private

Shareholders agreed to contribute to the equity interest of GISE, for the

purpose of creating the Investment Project described therein.

2. Pursuant to the terms of the CAE, the participation in the equity interest of

GISE on the part of FOCIR increased to $48,000,000.00 (Forty-eight million and

00/100 pesos).

3. As provided in the CAE, pursuant to the general ordinary shareholders meeting

of GISE, held February 21, 2000, formalized in public deed number 7452 before

Blanca Amalia Cano Garza de Bello, registered in the Public Notary Office number

187 of Ciudad Victoria, Tamaulipas, FOCIR took out 26,179,127 representative

shares of working capital of GISE without assigning a nominal value, paying as

consideration, on February 25, 2000 an amount of $30,000,000.00 (Thirty million

and 00/100 pesos).

4. In the general shareholders meeting referenced in the preceding paragraph,

the shareholders of GISE agreed to the increase of the variable working capital

of GISE up to the amount of $68,000,000.00 (Sixty-eight million and 00/100

pesos), authorizing the Board of Directors to issue the titles representing the

increase in working capital, and maintaining for such effects any unsubscribed

shares in the treasury of the company.

5. Pursuant to the above-referenced issue of shares, on June 30, 2000, FOCIR

contributed $13,116,000.00 (Thirteen million, one hundred sixteen thousand and

00/100 pesos) to the equity interest of GISE and on November 16, 2000

contributed $3,917,971.00 (Three million, nine hundred seventeen thousand, nine

hundred seventy-one and 00/100 pesos) comprising almost the total amount of

contributions to the equity interest of GISE committed under the CAE, and

increasing the share participation of FOCIR in GISE to $47,033,971.00

(Forty-seven million, thirty-three thousand, nine hundred seventy-one 00/100

pesos).

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6. Pursuant to the above-referenced contributions of FOCIR to the equity

interest of GISE, the Fund subscribed and paid for a total of 26,003,444

ordinary shares, nominally represented in the variable capital of the company,

of the 160,069,799 shares that represent the total of the equity interest

subscribed and paid of GISE as of the date hereof.

7. Pursuant to clause Fourth of the CAE, the participation of FOCIR would be

temporary and would remain effective for a period of nine (9) years, beginning

from the date of the first share contribution by FOCIR in the equity interest of

GISE, i.e. its equity participation would conclude on February 25, 2009.

8. Pursuant to clause Fourth of the CAE, the Private Shareholders have the

option to purchase in advance the shares repreentative of the capital stock of

FOCIR. Therefore, so as to accommodate the interest of the parties to the CAE

and party hereto; FOCIR, GISE, and UNIMARK executed a "Letter of Intent with

Terms and Conditions" (Carta de Intencion con Terminos y Condiciones) in which

they expressly, but not exclusively, set forth the terms and conditions by which

they agreed to implement and eventually to formalize the resolutions of each and

every obligation contained in such, as well as an acknowledgment of a debt

resulting from the purchase price of the representative shares of the equity

interest of GISE, property of FOCIR. A copy of such Letter of Intent is attached

hereto as Exhibit A.

9. Pursuant to an agreement by the General Manager of FOCIR, pursuant to the

powers granted by the H. Techical Committee, the disinvestment by FOCIR in the

equity interest of GISE, in the amount of $47,034,000.00 (Forty-seven million,

thirty-three thousand and 00/100 pesos), was authorized which represents the

"historic" value of the share participation of this Fund, under the credit

conditions set forth herein.

10. On August 2, 2004, GISE held at a General Shareholders Meeting, whereby,

among others, they adopted the legal and statutory resolutions necessary for

GISE and the Private Shareholders to execute this Agreement, as evidenced in

public deed number 13,344, granted before Mr. Francisco Hugues Velez, Public

Notary No. 212 of the Federal District.

RE P R E S E N T A T I O N S

1. FOCIR represents that:

(i) It is a Public Trust, organized by the Ministry of Finance and Public Credit

and Nacional Financiera, S.N.C. (Secretaria de Hacienda y Credito Publico y

Nacional Financiera, S.N.C.) under the laws of the United Mexican States, fully

authorized in accordance with its purpose to enter into this Agreement.

(ii) The legal representative has the legal capacity and sufficient authority to

execute this Agreement, which have not been revoked, modified or restricted in

any manner as of the date hereof.

(iii) Based on the representations and warranties of GISE and the Private

Shareholders, it is prepared to enter into this Agreement, on the terms and

conditions set forth herein.

2. THE PURCHASER represents that:

(i) It is a mercantile company duly organized and existing pursuant to the laws

of the United Mexican States, fully authorized in accordance with its corporate

purpose to execute this Agreement, as evidenced in public deed number 13,348

dated August 4, 2004, granted before Mr. Francisco Hugues Velez, Notary Public

number 212 of the Federal District, pending its registration.

(ii) Its legal representative has the legal capacity and sufficient authority to

execute the present Agreements, which, as of the date hereof, have not been

revoked, modified, or restricted in any manner, as evidenced in the

aforementioned public deed .

(iii) It agrees to execute this Agreement, on the terms and conditions set forth

herein.

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(iv) As set forth in the letters attached hereto as Annex "B", "GM", and "JMB"

have expressly and irrevocably waived (i) any right of first refusal granted to

them under article XIII of the By-laws of GISE to acquire, on a pro rata basis

to the number of shares held by it in GISE, the shares property of FOCIR,

representative of the capital stock of GISE, to be transferred in favor of THE

BUYER, as well as (ii) the procedure set forth in article XIII of the Bylaws of

GISE for the transfer of shares representative of its capital stock.

3. GISE represents that:

(i) It is a mercantile company duly organized and existing under the laws of the

United Mexican States, fully authorized in accordance with its corporate purpose

to execute this Agreement, as evidenced in public deed number 953 dated August

2, 1988 granted before Blanca Amalia Cano Garza de Bello, Notary Public

registered with the Public Notary Office number 187 of Ciudad Victoria,

Tamaulipas, registered on August 29, 1988 in the Public Registry of Property and

Commerce of Ciudad Victoria, Tamaulipas under number 65, Book 57, Commerce

Section.

(ii) Its Legal Representative has the legal capacity and sufficient authority to

execute the present Agreements, which have not been revoked, modified or

restricted in any manner as of the date hereof, as evidenced by public deed

number 13,348 dated August 4, 2004, granted before Mr. Francisco Hugues Velez,

Notary Public number 212 of the Federal District, pending its registration.

(iii) It agrees to enter into this Agreement, on the terms and conditions set

forth herein.

(iv) Its Federal Tax Registry is: GIS-880802-GH6.

(v) Its Shareholders Meeting dated August 2, 2004 authorized the transfer of

shares referenced to in the Clause Second hereof, so as to create an obligation

as set forth in the CAE, duly subscribed and signed by the Private Shareholders

and by GISE.

4. UNIMARK represents that:

(i) It is an American company, duly organized under the laws of the State of

Texas on December 31, 1991 and registered on January 3, 1992, in the Corporate

Section of the Secretary of State of Texas.

(ii) Its legal representative has the legal capacity and sufficient authority to

execute the present Agreements, which as of the date hereof, have not been

revoked, modified or restricted in any manner.

(iii) It agrees to execute this Agreement with FOCIR, pursuant to the terms and

conditions set forth herein.

(iv) It agrees to terminate the Trust referenced in Clause First hereof, as set

forth herein.

(v) It expressly and irrevocably waives (i) the right of first refusal granted

by article XIII of the by-laws of GISE, to acquire, on a pro rata basis to the

shares held by it in GISE, the shares owned by FOCIR representative of the

capital stock of GISE to be transferred in favor of PURCHASER, as well as (ii)

the procedure set forth in article XIII of the by-laws of GISE for the transfer

of shares representative of its capital stock.

Given the foregoing recitals and representations, the parties acknowledge

the capacity in which they act and agree and submit to the following:

C L A U S E S

FIRST. DEFINITIONS

The terms used herein and set forth below will have the following meanings,

whether plural or singular, capitalized or in lower case:

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Shares. Means the shares representative of the capital stock of GISE to which

Clause Second hereof refers to and that the BUYER buys from FOCIR.

Debt. Means the amount set forth in Clause Third Hereof, which represents the

amount that THE PURCHASER acknowledges is owed to FOCIR for the purchase of the

Shares, not including interest, expenses, premiums or any other amount generated

by the Debt itself.

CAE. Shall mean the Convenio de Asociacion Empresarial referred to in Recital 1

hereof.

CCP. Means the last rate (Costo de Captacion a Plazo de Pasivos en Moneda

Nacional) that Banco de Mexico deems representative of the collective of

multiple banking institutions, published in the Official Federal Gazette (Diario

Oficial de la Federacion) for the ordinary interest to the date on which each

Interest Calculation Period begins and for the moratory interest to the date on

which occurs the delay, recognizing that that both the ordinary and moratory

interests with vary monthly together with the variations of the CCP.

Agreement. Means this Stock Purchase, Debt Acknowledgment, Mortgage, and

Termination of Obligations Agreement.

Business Day. Means any day not considered a holiday in accordance with

applicable provisions of the Mexican Banking System.

Payment Date(s). Mean(s) the last business day of the month of October of each

of the years from 2004 to 2011.

Trust. Means the Irrevocable Guarantee Trust Agreement (Contrato de Fideicomiso

Irrevocable de Garantia) entered into on February 21, 2000 by and among the

Private Shareholders, GISE, and FOCIR with Banco Santander Mexicano, S.A.,

Institucion de Banca Multiple, Grupo Financiero Santander Mexicano, as trustee.

Notes. Mean the negotiable instruments to be subscribed by the BUYER duly

guaranteed by GISE in favor of FOCIR to evidence the Debt.

Interest Calculation Period. Means the period of time for which the interest

that accrue on the Indebtedness is calculated, the first Interest Calculation

Period commencing the day of execution hereof and ending the last date of such

month and each subsequent Interest Calculation Period beginning immediately

after the completion of the previous Interest Calculation Period and ending the

last day of such month and so on, recognizing that the computation thereof

includes all the days of the Interest Calculation Period, provided that the last

Interest Calculation Period of Indebtedness will end exactly on the date on

which the last capital amortization payment is made.

Outstanding Indebtedness. Means the amount of capital of the Debt that has not

been covered by THE BUYER in a specific date.

Cetes Rate. Means the average of the annual yield, equal to the discount of the

Federation Treasury Certificates (Certificados de la Tesoreria de la Federacion)

(Cetes) in the first exchange issued for a term of twenty-eight (28) days or for

a substitute term in the case of non business days, corresponding to the

auctions held during the immediately preceding month on the first date of each

Interest Calculation Period or on the date on which the delay occurs,

recognizing that both the ordinary and moratory interest will vary monthly

together with the variations of the Cetes Rate.

TIIE Rate. Means the Interbank Balance Interest Rate (Tasa de Interes

Interbancaria de Equilibrio) published periodically by Banco de Mexico in the

Official Federal Gazette (Diario Oficial de la Federacion) on the last day of

the preceding month, as well as of the date on which the first Credit

Disbursement (Disposicion de Credito) as well as on the date on which the delay

occurs, provided that the calculation of ordinary and moratory interests, as the

case may be, will be made monthly based on the last Interbank Balance Interest

Rate published in the preceding month, regardless of the term for which it was

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determined and if on such date various Interbank Balance Interest Rates for

various terms are published the following will apply: (i) the Interbank Balance

Interest Rate set for the term of twenty-eight (28) days; (ii) failing that,

that Interbank Balance Interest Rate for term of greater than twenty-eight (28)

days that is closest to the length of such term; and (iii) failing that, the

Interbank Balance Interest Rate for a term of less than twenty-eight (28) days

that is closest to the length of such term, recognizing that both the ordinary

and moratory interest rates will vary monthly together with the variations in

the TIIE.

SECOND. PURCHASE

In accordance herewith, in order to accommodate the interests of Unimark, GISE,

and FOCIR, THE PURCHASER purchases for FOCIR, which, in turn sells each and

every of its shares representing the equity interest of GISE duly subscribed and

paid for by FOCIR (the "Shares") as set forth below, for the price of

$47,034,000.00 (forty-seven million, thirty-four thousand and 00/100 pesos).

The Shares acquired by the PURCHASER are those represented by the following

share certificate:

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<CAPTION>

CERTIFICATE SERIES SHARES REPRESENTED AMOUNT

----------- ------ ------------------ ------

<S> <C> <C> <C>

9 B 26,003,444 N/A

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In connection herewith, FOCIR will deliver to THE PURCHASER the stock titles

described in this clause, duly endorsed in blank in its favor, for the purpose

of delivering the shares in connection with the purchase.

FOCIR and THE PURCHASER expressly agree that the purchase price of the Shares

will be paid to FOCIR within a maximum period of seven years, three months,

accrued beginning with the signature hereof, made in seven annual partial

payments in consecutive installments on the Debt Payment Dates, pursuant to the

conditions set forth in the Clause Sixth hereof.

As a result the execution of this Agreement, FOCIR grants to THE PURCHASER the

broadest receipt allowable by law with respect to the fulfillment of the

obligation delivery of the purchase price, on the understanding that as of the

date hereof THE PURCHASER acknowledges that it owes to FOCIR the amount of Debt,

same that amounts to the purchase price.

In virtue of the foregoing, GISE agrees to register the transfer of Shares

referred to in this clause in its Shareholders Registry Book.

THIRD. DEBT ACKNOWLEDGMENT

As consideration for the Purchase of the Shares referenced in Clause SECOND

hereof, THE PURCHASER expressly and irrevocably acknowledges that as of the date

hereof it owes to FOCIR the amount of $47,034,000.00 (forty-seven million,

thirty-four thousand and 00/100 pesos) (the "Debt"), on the understanding that

the Debt will accrue ordinary and moratory interest, as the case may be, from

the date of execution hereof at the interest rate and under the conditions set

forth in Clause Fifth hereof.

The amount of the Debt does not include interest and expenses arising from this

Agreement.

FOURTH. TERMINATION OF THE TRUST

As a result of the purchase of Shares referred to in Clause Second hereof,

FOCIR, in its capacity as Trustee, and UNIMARK, in their capacity as settlor,

who must obtain the consent of the rest of the settlers (the "Settlors"), hereby

demonstrate their express and irrevocable intent to terminate the Trust.

Considering the foregoing, the parties agree to notify the Trustee of their

decision to terminate the Trust, so that said institution, together with FOCIR

in its capacity as Trustee, and the Private Shareholders in their capacity of

Settlors, and pursuant to the provisions on fraction I of article 392 of the

General Law of Negotiable Instruments and Credit Transactions (Ley General de

Titulos y Operaciones de Credito), will

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carry out the corresponding termination, as well as see to other necessary

matters for the formalization of said termination and to conform to the

provisions of article 393 of the General Law of Negotiable Instruments and

Credit Transactions (Ley General de Titulos y Operaciones de Credito), the

return being in favor of the Settlors of the pledged interests, recognizing that

any expense arising in connection with the termination of the Trust will be

charged to the Settlors.

FIFTH. DEBT INTEREST

The Debt will accrue ordinary and moratory interest from the date of execution

hereof, which will be calculated on a basis of a year of three hundred sixty

(360) days and of days which have effectively elapsed.

A) ORDINARY INTEREST.

THE PURCHASER hereby agrees to pay to FOCIR on a quarterly basis, with