A dull, earthy [calcite] deposit, known as [caliche], occurs in areas of Texas that have scant rainfall, such as the [High Plains], west Texas, and the southwestern part of the [Gulf Coastal Plain]. Caliche commonly is found mixed with other materials, such as [clay], [sand], or [gravel]. This substance may be firm and compact or loose and powdery.
It is thought that [caliche] forms when ground moisture, containing dissolved calcium bicarbonate, moves upward. In dry areas of the country, this moisture evaporates. As it does, it leaves a crust of calcium carbonate in the form of caliche on or near the surface of the ground.
[Calcite] crystals (dog-tooth spar) from the Terlingua area of Brewster County, Texas.
[Caliche] is quarried in many counties in Texas and is used chiefly as road material and as an aggregate.
Caliche. See [Calcite].
Carnotite. See [Uranium Minerals].
Cassiterite
[Cassiterite], tin dioxide, is the mineral that serves as the chief source of tin. Tin does not corrode and tarnish, and one of its main uses is in the making of tin cans. (Actually, our tin cans are made from thin sheets of steel that have been coated with a protective layer of tin.)
[Cassiterite] has either a nonmetallic or a submetallic luster. Some specimens are brilliant and shiny; others are dull. Cassiterite may be [translucent] to [transparent]. It may be black, brown, gray, reddish brown, or yellowish brown. When rubbed across a [streak] plate, this mineral leaves a pale brown, a pale yellow, or a white streak. Cassiterite is quite heavy—it has a [specific gravity] of 6.8 to 7.1. It is too hard to be scratched by an average pocket knife.