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PRECIOUS STONES
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and
with borax melts with effervescence to a transparent glass. Color,
white, pale blue, green, or red; purple, pink, and lavender are found
in Massachusetts. Streak uncolored.
Serpentine is a deep green stone, very soft, and useless as a gem.
Smaragdite,
a variety of hornblende, is of emerald-green, gray, and greenish-gray
color. It is also found with pink and ruby corundum disseminated
through it. Consists of silica, alumina, magnesia, lime, soda, ferrous,
and other oxides. Hardness, 5.5; specific gravity, 3.12.
Sodalite
is found in dodecahedrons, like lapis lazuli. Hardness, 6; specific
gravity, 2.25 to 2.3. Composition: silica, 37.2; alumina, 31.7; soda,
19.1; sodium, 4.7; chlorine, 7.3. Color, gray, brown, violet to deep
azure-blue. Found in Greenland, Vesuvius, and in the State of Maine.
Spodumene,
or triphane, takes a high polish, but is difficult to work, being
harder in one direction than another, and of very easy cleavage.
Crystallization monoclinic, in modified oblique rhombic prisms.
Hardness, 6.5 to 7; specific gravity, 3.1 to 3.19. Surface of cleavage
pearly. The fragments in which it is usually found show two parallel
cleavage planes. Translucent to subtranslucent. Composition: silica,
alumina, lithia, and a small proportion of iron oxide and soda. Acids
do not attack it, but it fuses before the blow-pipe to a transparent
glass. Color, gray to greenish yellow. It is found in many localities
in Europe and the United States, but transparent only in Brazil.
Hiddenite is a variety of spodumene, containing about two per cent,
more lithia.
Staurolites, or staurotide, from the Greek stauros, a
cross. Crystallization trimetric, in right rhombic and six-sided
prisms. Some of the crystals are cruciform, having twinnings, or two
prisms crossing one another in the form of a cross. Hardness, 7 to 7.5;
specific gravity, 3.65 to 3.73. Cleavage imperfect. Lustre vitreous to
resinous; transparent to opaque. Color, reddish brown to black. Trans-
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