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144 THE DIAMOND MINES OF SOUTH AFRICA
covered
with irregular oval and half-round grooves of various depths. In one
experiment, the diamond was found to be deeply eaten away on one side,
so that the depression nearly penetrated through the stone.
Diamonds
thus magmatically corroded have a similarity, as regards the appearance
of the corrosion, to hornblende and kindred materials. A small spot or
scar was, at times, found at the bottom of a large indent. The diamonds
were usually found, after the experiments, to be blackened, or covered
with a red coating, which proved to be oxide of iron.
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Some
of the diamonds showed little black or greenish black balls located
exactly in the centre of the holes. The formation of the balls is
doubtless connected with the creation of the grooves. These little
balls are magnetic, and when treated with hydrochloric acid, in which
they are only partly soluble, they evolve a gas.
The
quantity of these balls was too limited to permit of any very exact
investigation of their nature. Herr Luzi presumes that they are
transformed diamond-carbon, i.e. a different modification of
carbon, which contains either oxide of iron or metallic iron reduced
out of the oxide. He was, however (owing to the
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