Fluorite
[Fluorite] is calcium fluoride. The fluorite that is mined and sent to market, however, commonly is found mixed with [quartz], [calcite], [limestone], or other rocks and minerals. Industry calls this mixture fluorspar.
[Fluorite] is a [transparent] to [translucent] mineral that has a glassy luster. It may be colorless, or it may be white, pink, green, purple, brown, or blue. Some specimens show more than one color. When you rub fluorite across a [streak] plate, it leaves a white streak. This mineral is not particularly hard—a pocket knife will scratch it, although a copper penny will not. Fluorite has perfect [cleavage] in four directions. By carefully breaking a specimen, you can obtain [cleavage fragments] that are shaped like [octahedrons].
[Fluorite] occurs as cleavable masses, as fine or coarse grains, and as crystals. Most of the crystals are [cubes], but some may be [octahedrons], [dodecahedrons], or combinations of these.
[Fluorite] has been found both in west Texas and in central Texas. In the [Llano uplift] area of central Texas, it occurs in a number of [Precambrian] [granite], [pegmatite], [schist], and [gneiss] rocks. The most important, although small, deposit in this area is near Spring Creek a few miles west of Burnet in Burnet County. Here, prospectors have dug holes and pits in gneiss and schist rocks and found layers of fluorite in them.
The largest known [fluorite] deposits in Texas (they are not particularly large when you compare them with the deposits in Illinois and Kentucky) are those in the Eagle Mountains of Hudspeth County. This fluorite occurs in both [igneous] and [sedimentary] rocks. Many years ago, probably during the late part of the [Tertiary] [Period], hot [magma] far below the surface gave off liquids and gases containing fluorine. These [fluids] moved up through large cracks (called [faults]) in [Cretaceous] limestones and Tertiary [igneous rocks] and deposited fluorite in them. In places, beds of [limestone] have been replaced by fluorite. Some of this west Texas fluorite has been mined and shipped to market.
[Fluorite] has octahedral [cleavage]. The four directions of perfect cleavage can result in [cleavage fragments] that are [octahedrons].
[Fluorite] is extremely important as a flux in steel-making to help the ingredients of the molten steel blend together. In addition, it combines with [sulfur], phosphorus, and other unwanted substances so that they can be removed from the steel. Other important uses of fluorite are in glass-making and in the manufacture of hydrofluoric acid. This acid is used in the aluminum industry as well as in industries that make high-octane gasoline, insecticides, and refrigerants for refrigerators and freezers.