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CHAPTER XIV
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DIAMONDS FOR MECHANICAL PURPOSES. ARTIFICIAL DIAMONDS AND DIAMOND WEIGHTS
IN
addition to carbonado or carbon, there are other forms of diamond which
are used largely for mechanical purposes. Of these the principal is
called " bort." This is crystallized diamond not sufficiently
transparent or clear to cut as jewels. A' large part of the product of
the diamond fields is composed of this material. It is estimated that
one-quarter of the yield of the Brazilian diamond fields and about
forty-five per cent, of the African mines, consists of bort. Some of
the African mines yield a larger proportion than others, notably, the
Premier and the Kimberley.
Usually
it is too brittle for drill purposes, the crypto-crystalline carbon
being harder and better able to resist pressure. Nevertheless, bort, in
sizes from one to three carats, is used to a certain extent in drills
which are not forced to any great depth, or through very refractory
strata.
Crystals
weighing one-half to one carat each are used extensively as teeth in
stone-saws for sawing marble and stone for building purposes. Revolving
saws up to 75 inches in diameter and sometimes over, carry up to 100
diamonds weighing in the larger sizes 25 or 30 carats worth $20 per
carat. These saws with a rim speed of 10,000 to 12,000 feet per minute,
cut into limestone over
315.
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