Corundum: Native
Crystalline Alumina. This mineral occurs in crystals, also massive and
granular, possesses a wonderful array of color including red, blue,
green, yellow, brown and gray, and ranks next to the Diamond in
hardness. Its hardness, together with its rich transparent colors,
makes it highly prized as a gem material The pure transparent
varieties, according to their color, are as follows: blue. Sapphire;
red, Ruby; yellow, Topaz; green, Emerald; purple, Amethyst. A variety
having a stellate opalescence is called a Star Sapphire. The finest
Sapphires are usually obtained from the beds of rivers. The best Rubies
come from mines in Burma, and one weighing 304 carats is said to have
been found there in 1890. In recent years "reconstructed rubies" have
become a recognized article of commerce. These are crystalline drops of
ruby colored corundum, made by melting the splinters and crystals of
the mineral in an electric arc. In the United States, corundum is found
in Maine, Connecticut, New York, Virginia, North Carolina, Georgia,
Colorado and California. It is used as watch jewels, meter bearings,
besides furnishing the impure variety known as Emery, which is used
extensively as an abrasive, and in the manufacture of cutting-wheels.
Covellite: Sulphur
34%, Copper 66%, Cupric Sulphide, sometimes called "Indigo Copper"
because of the deep blue color of its fresh fracture. It is an
important ore of copper, but comparatively rare. Covellite is the
result of the alteration of other ores of copper, and is often mixed
with Chalcocite, from which it has been derived. It usually occurs
massive although crystals are known. It is found in Chile, Bolivia, at
Butte, Montana, and in crystals in the lava of Vesuvius.
Crocidolite: A
mineral principally consisting of Silicate of Iron and Soda. It is an
asbestos-like mineral, of lavender-blue or dark-green color. The green
fibrous variety is called Cat's Eye, and the decomposed brown
crocidolite, is called "Tiger-Eye." It occurs in South Africa, in
Ontario, and in Rhode Island, Massachusetts and Colorado.
Crocoite: Lead
Chromate. This mineral is bright hyacinth-red and translucent with a
streak of orange-yellow. It is one of the sources of the metal
Chromium, and occurs in Hungary, Brazil, and in Arizona, U. S. A.
Cryolite: Fluorite
of Sodium and Aluminium. Usually occurs as a fine granular mass,
crystals exceedingly rare; color snow-white, inclining to red and
brown. Because of its
low index of refraction, massive specimens suggest masses of wet
