Ch. 8: Properties and Tests Diamonds Diamonds

Page of 153

Text size:



	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." 70

Page of 153