_Composition_: CaF₂. _Crystal system_: isometric. _Hardness_: 4.
_Specific gravity_: 3.0 to 3.25. _Luster_: vitreous. _Color_: violet,
blue, colorless, green, yellow, brown, rose, and crimson red.
_Streak_: white. _Cleavage_: four directions, octahedral, perfect.
_Fracture_: subconchoidal to splintery. _Tenacity_: brittle.
_Diaphaneity_: transparent to subtranslucent. _Refractive index_:
1.434.
Very fine green, transparent fluorite has been found near Voca, Mason
County. The fluorite occurs as vug fillings in pegmatites, associated
with crystals of pink microcline and colorless quartz. Most of the vugs
have been completely filled by the fluorite; therefore, crystals (fig.
15) of the fluorite are not too common. Masses of fluorite several
pounds in weight, rich green, and quite transparent have been found near
Voca. Transparent pieces an inch or more in diameter are common.
[Illustration: Fig. 15. Common crystal form of fluorite.]
Fluorite is much too soft for everyday use in jewelry and because of the
low refractive index does not yield brilliant faceted stones. The
perfect four-directional cleavage, relative softness, and brittle
tenacity of the mineral make it difficult to facet. Faceted stones are
seldom seen outside of collections. Cabochons are also difficult to cut
from this material, but the rich color obtained is ample reward for the
time and care necessary in cutting.
Fluorite occurs at several other localities in Texas, notably in
Hudspeth, Brewster, Presidio, Llano, and Burnet counties, but not
commonly in gem quality or colors that warrant its use as gem material.