Ch. 14: Mechanical Purposes, Artificial, & Weights

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	CHAPTER XIV

	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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