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                                                                     EXHIBIT 5.1

                          Morgan, Lewis & Bockius LLP
                              1800 M Street, N.W.
                             Washington, D.C. 20036

         December 27, 2000



         United States Lime & Minerals, Inc.
         13800 Montfort Drive
         Suite 330
         Dallas, TX  75240


         Re:      Registration Statement on Form S-3 under the Securities Act
                  of 1933, as Amended

         Ladies and Gentlemen:


                   We have acted as counsel to United States Lime & Minerals,
         Inc., a Texas corporation (the "Company"), in connection with the
         filing with the Securities and Exchange Commission (the "SEC"),
         pursuant to the Securities Act of 1933, as amended (the "Act"), and the
         rules and regulations promulgated thereunder, of a Registration
         Statement on Form S-3 (the "Registration Statement") for the purpose of
         offering 1,818,181 shares of common stock, par value $0.10 per share
         (the "Shares") of the Company, to be offered (the "Rights Offering") by
         the Company pursuant to subscription rights (the "Rights").



                  We have participated in the preparation of the Registration
         Statement, and we have examined the Restated Articles of Incorporation
         and the Bylaws of the Company, as amended to date, and such other
         documents, records, statutes and decisions as we have deemed necessary
         or appropriate for the purposes of the opinion expressed herein. As to
         matters of fact, we have relied on representations of officers and
         representatives of the Company. In our examination, we have assumed the
         genuineness of documents submitted to us as originals and the
         conformity with the original of all documents submitted to us as copies
         thereof.



                  Based upon the foregoing, we advise you that, in our opinion,
         when issued and delivered upon the exercise of the Rights in accordance
         with the terms and conditions of the Rights Offering as described in
         the Registration Statement, the Shares will be validly issued, fully
         paid and non-assessable.





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                  We hereby consent to the use of this opinion as Exhibit 5.1 to
         the Registration Statement and to the use of our name under the caption
         "Legal Matters" in the Prospectus. In giving this consent, we do not
         thereby admit that we are acting within the category of persons whose
         consent is required under Section 7 of the Act or the rules or
         regulations of the SEC thereunder.


         Very truly yours,




         /s/ Morgan, Lewis & Bockius LLP