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.
