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196
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Spinel and Balas.
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from
the true or Oriental Ruby, with which it has been sometimes confounded.
It may also be distinguished by its inferior hardness, and specific
gravity.
A
peculiarity of Spinel is that the light which is reflected from the
depth of the gem, no matter what the colour of the stone, is always of
a pale yellow. The lustre is vitreous, and the gem displays every
degree of transparency. The refraction is simple. It is rendered
electric by friction, but not by heat ; differing in the latter respect
from Topaz, which is distinctly pyro-electric.
In the International Exhibition of 1862 there were two very fine Spinels ; one from India was cuf en cabochon forming
an octagon-shaped stone, of perfect colour, and free from flaws. It
weighed 197 carats. This was cut to an 81-carat "perfection stone." The
other Spinel was also an octagon-shaped stone, of perfect colour, very
" spread," and free from flaws. It weighed 102-1/4 carats, and was
re-cut, weighing after cutting 72-1/2 carats. It is strange that both
these stones arrived from India in the same year, viz., 1861.
In
the Ruby mines of Upper Burma, Spinel is a very common mineral, forming
in many cases a conspicuous part of the gem-bearing detritus. Fine
octahedral crystals have been found embedded in the calcspar, in which
the true Rubies occur, and it is also found in beautifully sharp
octahedra, and in flat hemitrope crystals, of small size, associated
with Rubies in the Ruby-earth.
Spinel
also occurs in Afghanistan in crystalline micaceous limestone. There
are famous mines of Balas Rubies at Badakshan in Uzbekistan, a part of
Tartary. The mines were known to the Emperors of Delhi. They are near
the Oxus, not far from Shighnan. There is a belief among the natives
that two large Rubies always lie near each other : thus it is that the
fortunate finder of
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