optical density optical separator orange Orange River Oranjemund
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Sunday, 23 September 2007

optical density. See optically dense, re-

I RACTIVE INDEX.

optical separator. A device devel­oped by the diamond Research Lab­oratory, Johannesburg, Republic of South Africa, for the recovery of Diamonds from worthless material. It is based on the difference between the light-reflecting properties of dia­monds and other gravel constituents.

See diamond RESEARCH LABORATORY.

orange

diamond. A diamond of a distinct orange tint. It does not refer to a diamond from the Orange River Valley, although most stones of this color are found in the Republic of South Africa. Many of them are red­dish orange-brown, somewhat simi­lar to the color of some zircons. Others are a more vivid reddish-orange color, reminiscent of flame spinel. Some vivid deep-orange dia­monds have been found in the Wes-selton Mine. Few of these Diamonds reach the North American trade. They are properly called fancies.

Orange Free State. A province in the Republic of South Africa, south of the Transvaal, that was formerly a vir­tually independent colony of Boers. Some important diamond mines, such as Jagersfontein and Koffiefon-tein, are located in the province. Al­luvial production from the Orange Free State has practically ceased, however.

Orange River. The principal river in the Republic of South Africa along


which, together with its main tribu­tary, the Vaal, are located many of the country's alluvial diamond depos­its. It forms the boundary between South-West Africa and the Republic of South Africa, and rises in Lesotho (formerly Basutoland). The first large white rough diamond, the 83.50 carat Star of South Africa or Dudley diamond, found in the Orange River, was fashioned into a 47.75-carat oval brilliant.

Orange Tiffany diamond. See tiffany

diamond.

Oranjemund. A town about five miles north of the mouth of the Or­ange River that is maintained by Consolidated diamond Mines of South-West Africa, Ltd., for its em­ployees. Important mining activity is carried out not far to the north. See

SOUTH-WEST AFRICA.

Orapa pipe. The world's second largest known kimberlite pipe, de­signated 2125 AK/1. It is part of the Letlhkane group of kimberlites, lo­cated in the area of Orapa on the eastern edge of the Kalahari desert, about 210 miles north of Gaborone, the capital of Botswana. The Orapa pipe was discovered by the De Beers prospecting team, in 1967, under the sands and gravels of the Kalahari desert. Officially opened on May 26, 1971, it came into production July 1, 1971. It is oval in plain view, 1.2 km. x 1.61 km., with a surface area of 113 hectares (280 acres), and re­ported to be about 5,000 feet deep. The preliminary assessments indicate a ratio of Gemstones to industrial Diamonds of 10 to 90, respectively. Ore reserves have been proven to 37 meters depth (about 120 feet) which