Garnet.—Deep-red
rounded grains of clear pyrope are abundant in the ' blue ground,' and
these, with black grains of titanic iron, remain with the diamonds in
the final washings. Pyropes are also seen imbedded in the dark green
peridotite rock. They have been utilised as gems. The pyropes which
were observed in thin sections were isotropic, nearly pure and always
rounded. In one case a pyrope was surrounded by a zone of
magnesia-mica. Cracks penetrate the pyropes irregularly, as is usual.
Another
variety of garnet occurs, which greatly resembles the diamond. These
garnets are very small, colourless, or with a faint tinge of green, and
have such a high index of refraction that it is difficult to see their
shape. They are crystallised apparently in forms strongly suggesting
the diamond, the faces being sometimes curved, and the octahedral
forms apparently predominating. They are unattacked by acids, including
hydrofluoric acid. They melt readily to glass in a crucible, and may
thus be distinguished from diamonds. Most of them are so small as to
be seen only with high powers, and they are then readily confounded
with minute diamonds. They probably belong to the variety of garnet
called ' demantoid,' ' which is found in the diamond
