28                 THE MATRIX OF THE DIAMOND name of ' Vaalite.' In this state it is a soft yellow or bluish-green micaceous mineral, containing nearly 10 per cent, of water.
	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