In many cases bauxite resembles limonite in being a mixture of two or more aluminum oxides with water of crystallization, such as Al₂O₃·H₂O, Al₂O₃·2H₂O and Al₂O₃·3H₂O. This is particularly true of the bauxite which resulted from the decomposition of rocks by surface water.
Bauxite is the ore from which aluminum is obtained. The deposits are not large, but the United States has its share of them. It is found in Alabama, Arkansas, Georgia, Missouri, Tennessee, and California.
[Cryolite]
Na₃AlF₆
Ice stone
Occurs in pseudo-cubic crystals or massive; hardness 2.5; specific gravity 3; color white; luster vitreous; transparent on thin edges.
Cryolite is a relatively soft mineral, colorless to white as snow; for which reason, and partly also because it comes mostly from Greenland it is called “ice stone.” It is really monoclinic but the inclination of the c axis is so slight, that, unless examined carefully, the crystals appear to be cubic. Until about 1900 great quantities of this mineral were shipped from West Greenland, and from them the metal aluminum was extracted. When bauxite was discovered, it was found to be considerably cheaper to make the aluminum from that mineral, and now cryolite is no longer sought. Aside from its occurrence in Greenland some cryolite is found in Colorado, near Pike’s Peak.
The Arsenic Group
The metal, arsenic, is a dark steel gray in color, when the surface is fresh, but it soon tarnishes. It is very brittle and easily powdered under the hammer, and its only use as a metal, is for an alloy with lead in making shot. Its compounds find a wider use. The white powder called “arsenic” is arsenous acid, and is used mostly in making poisons, which fortunately are easily detected in animal tissues. Copper arsenate, (Scheele’s green) is a pigment used in making green paint, and formerly in the green colors of wall paper. A combination of arsenous acid, copper oxide and acetic acid is the well known Paris Green, so much used for an insecticide. Beside these uses, arsenic serves a large number of other purposes, as in making glass and enamel, embalming fluids, and various medicines.
Curiously arsenic plays a double part, acting part of the time as a metal, as in the two following minerals, and part of the time as a non-metal, as in cobaltite, niccolite, etc.
[Arsenopyrite]
FeAsS
[Pl. 24]
Occurs in well formed crystals, grains, or masses; hardness 5.5; specific gravity 6; color silver-white; streak black; luster metallic; opaque on thin edges.