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PRECIOUS STONES.
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addition
to the Ruby, Sapphire and other gem varieties of Corundum. In Siam the
associates are Sapphire, Quartz, Ilmenite and Zircon. In Ceylon the gem
sands contain, besides the Ruby, Sapphire, and other varieties of
Corundum, Garnets, Zircon, Quartz, Chrysoberyl, Magnetite, Amethyst,
Tourmaline, Spinel, etc.
In
North Carolina the associated minerals are Garnet, Spinel, Monazite,
Rutile, Ilmenite, different Micas, Stauro-lite, Gold, etc., and the
Rubies often show inclusions sometimes so minute as to give the gem a "
sheen " (Judd and Hidden).
The
mining of the Ruby in Burma is now carried out by the Burma Ruby Mines,
Ltd. Here not only open workings are found, but also tunnels driven in
to cut the gem-bearing material, which is washed to free it from as
much earthy matter as possible, the remaining gravel containing the
Rubies being afterwards picked over by hand. The machinery, which is
somewhat similar to that employed in Diamond washing, is now driven by
electricity, transmitted from some distance.
It
has already been remarked that the colour of a Ruby varies with the
direction in which it is viewed; the richest colour is seen on looking
along the principal axis of the crystal, hence, in cutting, the gem
should be so fashioned that this axis is presented to the eye of the
observer, the table thus being parallel to the basal face of the
crystal. The gem is usually cut as a brilliant. Some few Rubies show
asterism, and are cut en cabochon, but this is not nearly so
frequently seen in Ruby as in Sapphire. More rarely step cut stones are
seen, or those in which the form of the crown is that of a brilliant,
while the culasse is
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