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PRECIOUS STONES
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consumed
while the air is excluded, it becomes coated with graphitic carbon.
Strongly heated and thrown suddenly into liquid oxygen, the diamond
burns brilliantly and yields, by its oxidation, carbonic acid.
In
oxygen, under a powerful lens, the diamond becomes clear red. Soon
after, it is apparently enlarged in bulk, being surrounded by a faint
white light, the result of combustion. Black spots appear on the
surface, especially if the heat is diminished. If the heat be
continued, it will be entirely consumed, but if the heat be withdrawn,
it will immediately cease to burn.
A
diamond placed in a muffle previously heated red-hot soon acquired the
same color, and a few seconds later became conspicuous by a bright
glow. On being then removed, it had a slight milky appearance.
There
has been much speculation and many theories about the processes by
which carbon was gathered and crystallized, but authorities concur in
the opinion that the result was attained by an exceedingly slow
process and under tremendous pressure. It has been demonstrated, also,
that the physical condition of carbon depends somewhat on the pressure
to which it is subjected at the time of consolidation.
Carbon
in the adamantoid form has been obtained by saturating iron with pure
carbon and subjecting the molten mass by various processes to great
pressure, but the results have not been sufficient to demonstrate with
certainty how nature secured the material of which the diamond is
composed, or the exact methods used in the transformation.
Diamantoid
carbon has been discovered in meteoric iron. Carbonado was found in a
meteorite which fell in Russia in 1886; and in 1890 particles were
found in meteoric iron in Arizona, which were, after careful
examination, pronounced to be diamonds.
Some have adopted the theory that pure carbon was separated by electricity from carbonic acid, and after absorption
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