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THE BOOK OF DIAMONDS
ness.
Stones from wet diggings are usually harder than those from dry
diggings. African diamonds are softer than Brazilians; Indian are
harder, and those of Borneo and Australia are said to be the hardest of
all. The skin of a crystal, or outside, is harder than the inside, and
frequently there are knots in the grain, so much harder that it is
difficult to cut them. The wheel makes very little impression when
cutting against the grain of the diamond. It must be cut across the
grain.
The
only rival of the diamond in hardness is the metal tantalum, of which
it is said that in the effort to bore a hole through a plate of it, a
diamond drill driven at the rate of 5,000 revolutions per minute for
three days and nights, made a depression one-fourth millimeter deep.
Graphite
and diamond pass insensibly into one another. Hard graphite and soft
diamond are near the same specific gravity. The difference appears to
be one of pressure at the time of formation. Graphite may be attacked
by fuming nitric acid and potassium chlorate.
Diamond
is the hardest, the most imperishable, and also the most brilliant of
minerals. Nothing will cut diamond except diamond. Nothing will cut so
well; nothing drills porcelain so neatly; and the dentist will tell you
that when he uses a whirling instrument of torture for hollowing out a
cavity, he is using a diamond on your tooth.
Charles
Kingsley once said: "We may consider the coal upon the fire as a middle
term of a series of which the first is live wood and the last diamond."
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