<Li> Common opal occurs on the Texas Coastal Plain . </Li> <Li> Salts occurs in large quantities in salt domes in the Texas Coastal Plain and with other evaporites in the Permian Basin of West Texas, as well as near Grand Saline, Texas . </Li> <Li> Sands used for industrial purposes commonly have been found in the Texas Coastal Plains, East Texas, north central Texas, and Central Texas . </Li> <Li> The discovery of silver in Texas has been credited by some to Franciscans who discovered and operated mines near El Paso about 1680 . Documented silver production started in the late 1880s at the Presidio Mine, in Presidio County . Texas produced 32,663,405 troy ounces of silver between 1885 and 1955 </Li>

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