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PRECIOUS STONES
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RUBY
Is
a corundum, of which the red are called rubies, and blue and other
colors, sapphires. The deep, clear red is known commercially as Burmah
or Oriental ruby; the pink, as Ceylon ruby; and the dark garnet-red, as
Siam; the colors being usually found in the localities with which they
are coupled.
Crystallization hexagonal, occurring in six-sided prisms, and usually found as rolled fragments.
Hardness, 8.8 to 9; very tough when compact; specific gravity, 3.97 to 4.05.
Lustre
vitreous; sometimes pearly on the basal planes; transparent to
translucent; phosphoresces with brilliant red glow when exposed to
electric discharge in high vacuo; electric by friction, retaining it
for several hours.
Cleavage perfect, parallel to basal plane; fracture con-choidal and uneven; brittle.
Doubly
refractive (index, 1.77 and 1.76) ; dichroic, twin colors of Burmah,
crimson and aurora-red; of Siam, crimson and brownish red.
Composition: pure alumina.
In combination with borax it melts with difficulty into a clear glass. Is unaffected by chemicals.
Color, various shades of red; gem color, blood-red; streak, white.
Cut step and en cabochon.
Symbolizes charity, dignity, divine power, July.
Star ruby is a variety having fine striations on the basal plane. When cut en cabochon, with the top of the convex surface at the intersection of these lines, a chatoyant star appears.
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