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beds of limestone have been replaced by fluorite.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.
[Illustration: 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.