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Carbonado - the toughest diamond

Posted September 24th, 2008 by admin

Carbonado, which comes mainly from Brazil, is the toughest variety of diamond, but it is far less plentiful than boart. Corundum, when used as an abrasive, is dull gray or brown in color, nontransparent, and it is largely imported from the Transvaal. Much’of this is exported to the U.S.A. for use in grinding wheels.
Emery is a close mixture of granular corundum and magnetite. Deposits occur as pockets in crystalline limestone, or as residual deposits after the removal by weathering of such rocks. This material is found in the island of Naxos (Grecian Archipelago), Turkey (the province of Aiden in Asia Minor), and in the central Urals (U.S.S.R.). Those garnets which include iron are chiefly used for grinding and polishing, and the most important deposits are found in the Adirondacks, U.S.A.

The working of stones by which their natural surfaces are improved dates back to many centuries. The art reached a high standard in Egypt over 5000 years ago, and it is known that the Egyptians worked comparatively hard stones, such as quartz, by pounding and rubbing with a stone held in the hand. Sawing was carried out by means of a copper blade, together with the help of an abrasive power. These processes are represented in many tomb paintings.