Epidote.

Epidote. Under this name are included several minerals, which are of some importance as rock-formers. Only two need be mentioned here, Zoisite and Pistazite, or Epidote proper. Zoisite, or lime-epidote, is a silicate of alumina and lime, the alumina sometimes being replaced by ferric oxide to the extent of 2 or 3 per cent. It crystallises in rhombic prisms, which are often curved or sharply bent. Usually it occurs as large imbedded crystals or as foliated and columnar aggregates, chiefly in crystalline schists, especially such as are rich in amphiboles. It is generally light-coloured—white, yellowish, or brownish-gray. Its hardness = 6½. Pistazite, or epidote proper, is a silicate of alumina and lime in which the alumina is replaced by ferric oxide up to 17 per cent. or thereabout. Hence it is often spoken of as iron-epidote. It has a peculiar dark yellowish-green colour, known as pistachio-green. It crystallises in monoclinic prisms, and has a hardness similar to that of zoisite. The largest and best developed crystals are met with amongst the crystalline schists and gneisses, and not infrequently in metamorphosed limestones. In eruptive rocks it occurs only as a decomposition-product after pyroxenes, amphiboles, micas, and feldspars.