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PRECIOUS STONES
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161
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TOPAZ
Was found in old times on a foggy island in the Red Sea, difficult to find, and the stone was named from the word topaso, to
seek. It is found now in Brazil, Russia, Saxony, Bohemia, Great
Britain, Egypt, New South Wales, Madeira, and the United States.
Crystallization trimetric, in right rhombic prisms with dissimilar pyramidal ends. Found often as rolled pieces.
Hardness, 8; specific gravity, 3.5 to 3.56; slightly higher in the colorless than in the colored.
Lustre vitreous; transparent to subtranslucent.
Cleavage perfect basal; fracture subconchoidal, uneven.
Double
refraction (index, 1.63 and 1.62) ; dichroic; twin colors of yellow,
yellow and rose-pink; electric by friction or heat (pyro-electric),
retaining electricity for many hours.
Composition varies: alumina, 57.5; silica, 34.2; fluorÂine, 15.
Infusible
before blow-pipe alone; melts with borax to white bead; dissolves in
salts of phosphorus, and is attacked by sulphuric acid; it changes
color under heat, and is liable to crack and flow by the action of fire.
Color,
white, light green and blue, pink, straw, yellow, orange approaching to
red; some are changed by heat to a wine-yellow or pink; streak white.
Cut step; in the United States, generally brilliant.
Symbolizes friendship, happiness, November, James the Younger.
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