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Sec. II, Ch. 2: The African Diamond

Sec. II, Ch. 2: The African Diamond Page of 366 Sec. II, Ch. 2: The African Diamond Text size:minus plus Restore normal size   Mail page  Print this page
84
African Diamonds.
upper part of the rock was oxidised by meteoric agencies, and was known, from its color, as "yellow earth." This passed downwards into the " blue ground," the colour of which suggests that the iron present has not reached the condition of peroxide.
The exact nature of the blue earth puzzled petrologists for a long time ; but the rock was carefully examined by Prof. Nevil Story-Maskelyne, and afterwards on the Contin­ent by many petrographers, especially by Cohen and Stelzner in Germany, and by Fouqué and Levy, in France ; and more recently in this country by Prof. Bonney and Miss Raisin. The late Prof. Carvill Lewis suggested that the blue Diamond-bearing rock should be distinguished under the name of Kimberlite. The base of the rock is generally a soft mineral, soapy to the touch, and of green or bluish color. By the late Prof. A. Stelzner, of the Mining Academy of Freiberg in Saxony, the blue matrix was re­garded as an altered olivine-diabase ; the whole rock being more or less serpentinized. The diamant iferous material in the pipes is however, not a distinct species of rock, but a mixture—partly of matter erupted from below and partly of altered sedimentary rocks. It contains angular fragments of shale, associated with various minerals, such as pyrope, or chrome-garnet, chrome-diopside of bright green colour, enstatite, mica, vaalite, zircon, cyanite, hornblende, barytes, magnetite, chromite, titaniferous iron-ore, perofskite, etc.
But the only minerals that attract the miner's attention are the Diamonds. These are sparkling pretty freely through the " stuff ; " sometimes as beautifully formed crystals, but frequently as mere fragments and splinters. They are said to be most abundant in the neighbourhood of doleritic dykes, but their distribution is very irregular ; in one claim they may be richly disseminated, whilst in the neighbouring
Sec. II, Ch. 2: The African Diamond Page of 366 Sec. II, Ch. 2: The African Diamond
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