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PRECIOUS STONES
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Pyrite
is sulphide of iron. A variety which is found in crusts of small,
brilliant crystals, is trimmed and cut into various shapes for jewelry.
These and some larger single crystals are found in Pennsylvania.
Crystals sufficiently compact to be faceted have been found in
Colorado and sold in Europe under the name of marcasite.
Rhodonite
is a manganese spar used largely in Russia as an ornamental stone.
Crystallization monoclinic, in oblique rhombic prisms. Hardness, 5.5 to
6.5; specific gravity, 3.6 to 3.7. Cleavage indistinct. Lustre
vitreous; transparent to opaque. Very tough. Composition : silica,
39.6; manganous oxide, 52.6; ferrous oxide, etc., 7.8. It blackens with
exposure, turns brown when heated, and fuses to a hyacinth bead in the
outer flame. Color, flesh to light red. Found in Sweden, Russia, and
the United States.
Rutile
is pure titanium oxide. Crystallization dimetric, in prisms of eight,
twelve, or more sides, with pyramidal terminations, and often bent.
Hardness, 6 to 6.5; specific gravity, 4.15 to 4.25. Cleavage lateral.
Lustre submetallic; transparent to opaque. Some transparent stones have
been cut. Composition: titanium, 61; oxygen, 39. Infusible before the
blow-pipe alone, but melts to a red bead with borax. Color, black and
red. The crystals are often found embedded in a compact red oxide of
iron. Long, slender crystals occur in the body of rock crystal, in
which case it is called " Venus's hair stone," and " love's arrows." It
is found in Europe, Georgia, North Carolina, Connecticut, and Colorado.
Cut black rutile strongly resembles the black diamond.
Scapolite
is found in Norway, Sweden, Finland, at Vesuvius, and in the Eastern
United States. Crystallization dimetric, in modified square prisms,
often terminating in pyramids. Hardness, 5 to 6; specific gravity, 2.6
to 2.75. Lustre pearly; transparent to opaque. Cleavage indistinct
parallel to lateral planes. Composition: silica, 48.4; alumina, 28.5;
lime, soda, etc., 23.1. Fuses slowly before the blow-pipe,
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