In this country this complex phosphate of aluminum and copper is found in streaks and patches in volcanic rocks, but in Persia comes from metamorphic rocks. To the Persians it was a magical stone, protecting the wearer from injuries, and among the Pueblo Indians it was regarded as of religious value in warding off evil. The best turquois comes from Persia, but it has been found at several points in the United States, as in Los Cerrillos and Burro Mts., N. M., in Mohave Co., Ariz., San Bernardino Co., Cal., in Nevada and Colorado.
Fluorine
At ordinary temperatures the element fluorine is a colorless gas, which was not obtained pure until 1888, because it could not be contained in vessels of glass, gold, platinum, etc. At that time it was made and kept in a vessel composed of an alloy of platinum and iridium. Its most important compound is hydrofluoric acid, a fuming liquid, which is mostly used to etch or dissolve glass. It occurs in several minerals, like tourmaline, turquois, etc., but the only one used to obtain the hydrofluoric acid is fluorite.
[Fluorite]
CaF₂
[Pl. 50]
Fluor spar
Occurs in crystals and cleavable masses; hardness, 4; specific gravity, 3.2; colorless or some shade of violet, green, yellow, or rose; luster vitreous; transparent on thin edges.
Fluorite usually occurs in beautiful cubic crystals, often with the edges and corners beveled by smaller faces, and occasionally in twins, which seem to have grown through each other. There is perfect cleavage parallel to each of the octahedral faces, which often, as in the illustration on [Plate 50], show as cracks cutting off the corners.
Since fluorite loses weight and color on heating, it is concluded that the colors are due to the presence of hydrocarbon compounds. The red and the green fluorite when heated to above 212° F. become phosphorescent, as may be seen if they are thus heated and exposed to the light, then taken into the dark.
Fluorite is quite commonly the gangue mineral associated with metallic ores, and is also likely to occur with topaz, apatite, etc. It is generally in such places that it seems to have been deposited from hot vapors, rising from igneous magmas.
It is the only mineral at all common from which fluorine can be obtained, and is used for making hydrofluoric acid, and other chemical compounds of this element. It is, however, of much greater importance as a flux in reducing iron, silver, lead and copper ores. In the industries it finds a place, being used to make apochromatic lenses, cheap jewelry, and for the electrodes in flaming arc lamps.
Fluorite is widely distributed, some of the better known localities being Trumbull and Plymouth, Conn., Rossie and Muscalonge Lake, N. Y., Gallatin Co., Ill., Thunder Bay, Lake Superior, Missouri, etc.