Octahedra Gem
Octahedra Gem
Octahedra Gem
What Is Diamond? Where Is It Found?
What is Diamond?
Diamond is a colourless exceptionally hard mineral (but often tinted yellow, orange, blue, brown, or black by impurities), found in certain igneous rocks esp. the kimberlites of South Africa. It is used as a gemstone, as anabrasive, and on the working edges of cutting tools. Composition: carbon. Formula: C. Crystal structure: cubic. Name derived from the Greek adamas meaning invincible. Relative density 3.50- 3.52. Cleavage eminent along octahedral faces. Fracture conchoidal. Tenacity brittle. Lustre brilliantly adamantine. Refractive index 2.417- 2.419. Birefringence and pleochroism: none (cubic). Dispersion strong 0.044. Diamond crystals form as cubes, octahedra , the most common gem form, and dodecahedra. Colourless to Yellow Diamonds which have a strong absorbtion line in the violet end of the spectrum are members of the Cape series. Where is it found?
The most famous diamond bearing country is South Africa. The first diamond was reported in 1866. By 1869 an 83.5 carat diamond had been found and was named The Star of Africa. It was subsequently cut into a Pear Shape brilliant weighing 47.74 carats. The Golconda area of Southern India has been the source of somefamous diamonds such as the Koh-i-nor (mountain of light 186cts cut to 108.92 cts and now in the Tower of London) and Jehangir. Diamond is widespread in Brazil, most stones being small but of good gem quality. Alluvial diamonds have been found in most states of the USA. White and fancy coloured diamonds such as pinks and pinkish browns are mined at Argyle in North Western Australia. Other important producers are Russia, now the fourth largest producer, and China.
By weight the top ten producers in 1994 were: By Value The top ten were: Australia Botswana Zaire Russia Botswana South Africa Russia Zaire South Africa Australia South America Namibia Angola Angola Namibia South America Ghana Guinea Guinea Sierra Leone
Estimated 2001 Diamond Production by Country Country Carats
(‘000) Value
($ m) Botswana 26,416 2,194 Russia 20,500 1,650 South Africa 11,301 1,145 Angola 5,871 803 D.R. Congo 19,637 496 Canada 3,685 531 Namibia 1,502 322 Australia 26,070 294 Guinea 754 128 Sierra Leone 375 68 Central Africa Republic 614 92 Venezuela 325 41 Tanzania 191 28 Brazil 550 22 Liberia 155 23 Ivory Coast 145 17 China 150 15 Ghana 450 11 Lesotho 20 4 Guyana 20 2
Total 110,176 7,253 *Source: Mining Journal, London, August 23, 2002
Current Annual Production at World's Major Mines, 2001
Country
Carats Tonnes US$/carat Value (‘000) (‘000) ($ m)
Canada
Ekati 3,685 3,685 144 531
Botswana
Jwaneng 12,339 8,920 110 1,357 Orapa 13,056 15,779 50 653 Letlhakane 1,021 3,625 180 184
South Africa
Venetia 4,977 4,602 85 423 Namaqualand 808 6,083 180 145 Finsch 2,465 4,768 70 173 Premier 1,637 3,102 75 123 Kimberley 550 3,766 110 61 Baken 65 5,835 400 26 Koffiefontein 145 2,299 225 33
Russia
Udachnaya 11,500 9,000 85 978 Jubilee 5,500 9,100 65 358
Australia
Argyle 26,000 15,100 11 286 Merlin 70 270 110 8
Namibia
Namdeb Onshore 1,385 21,867 220 305
**Source: Mining Journal, London, August 23, 2002
How diamonds are formed?
Diamond is formed at great depth in the earth, between 150 and 300 km below the surface and at great temperatures and pressures. By a kind of volcanic eruption the diamonds were pushed up through volcanic pipes of diamond bearing rock such as kimberlite. With gradual erosion kimberlite chimneys were exposed at the earths surface.
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Pinkki - an Octahedral Gem