30 U.S.C. § 611: Common varieties of sand, stone, gravel, pumice, pumicite, or cinders, and petrified wood

No deposit of common varieties of sand, stone, gravel, pumice, pumicite, or cinders and no deposit of petrified wood shall be deemed a valuable mineral deposit within the meaning of the mining laws of the United States so as to give effective validity to any mining claim hereafter located under such mining laws: Provided, however , That nothing herein shall affect the validity of any mining location based upon discovery of some other mineral occurring in or in association with such a deposit. “Common varieties” as used in this subchapter and sections 601 and 603 of this title does not include deposits of such materials which are valuable because the deposit has some property giving it distinct and special value and does not include so-called “block pumice” which occurs in nature in pieces having one dimension of two inches or more. “Petrified wood” as used in this subchapter and sections 601 and 603 of this title means agatized, opalized, petrified, or silicified wood, or any material formed by the replacement of wood by silica or other matter.