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CHAPTER II.
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Corundum, Sapphire, Ruby, Oriental Topaz, Oriental Emerald, Diaspore, and Spinel.
C
ORUNDUM is nearly pure alumina (Al2 03),
and is found in almost all colors of the rainbow. The transparent
varieties rank among the most valuable of gems. The names, ruby,
sapphire, oriental amethyst, oriental emerald, and oriental topaz are
given to the transparent red, blue, purple, green, and yellow varieties
of the mineral. These colors are due to the addition of minute
quantities of metallic oxides to the alumina. Its specific gravity
varies from 3*97 to 4/05, and its hardness is 9 ; that of the ruby is
generally about 8'8. The finest pigeon's-blood-colored rubies are found at Man-dalay in Burmah, where mines have recently been leased by a London
syndicate. Fine rubies, which are generally small, sometimes of a pink
color, and often with a currant-wine or purplish tint, are found at
Ratnapoora in Ceylon ; likewise in Siam, where, however, the color is
most commonly a dark red, almost that of a garnet, often with a tinge
of brown. The finest sapphires are found in Burmah or Ceylon. Some of
the finest cornflower blue varieties are from Ceylon. Many of the rich
velvety blue, as well as the lighter-colored stones, are from the Simla
Pass in the Himalayas. Fine sapphires have recently been found in Siam
and in Australia, the latter generally of an opaque, milky-blue color.
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