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PRECIOUS STONES
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ness,
6.5 to 7, and brittle; specific gravity, 3.27. Lustre vitreous;
transparent to subtranslucent. Cleavage indistinct. It is trichroic and
pyro-electric. Composition: silica, 43.68; boron trioxide, 5.61;
alumina, 15.63; iron sesquioxide, 5.45; manganese sesquioxide, 3.05;
lime, 20.92; magnesia, 1.70; potash, 0.64. It is not attacked by acids,
but fuses easily under the blow-pipe to green glass. Color,
clove-brown, blue, and gray.
Azurite
is a deep blue form of copper ore, found in the upper part of ore-beds.
Crystallization monoclinic, in short, stout, modified rhombic prisms
massed together. Hardness, 3.5 to 4.5; specific gravity, 3.5 to 3.8.
Lustre vitreous ; transparent to nearly opaque. Consists of copper
oxide, 69.2; carbonic acid, 25.6; water, 5.2. When found in connection
with malachite, the two minerals are cut together en cabo-chon across the bandings, producing a beautiful and striking contrast.
Beryllonite
was thought, from its transparency, brilliancy, and form of
crystallization, to be topaz. It is found only in Maine. Hardness, 5.6
to 6; specific gravity, 2.8. It contains cavities filled with water or
carbon dioxide.
Bowenite is a white, and light to dark-green variety of serpentine.
Brookite
is similar to rutile. Flat, ruby-red, and honey-yellow crystals, at
times transparent. They have been found in the United States, but they
cannot be easily polished. Hardness, 5.5 to 6; specific gravity, 3.8 to
3.9. Anatase and arkansite are practically the same mineral. The
crystals are usually thin, hair-brown, and nearly transparent.
Calcomalachite
is a slightly harder variety of malachite, consisting of equal parts
carbonate of lime and carbonate of copper. It takes a high polish.
Cancrinite is found in Maine. There are three varieties, —orange-yellow, cleavable and transparent in thin frag-
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