What is "epidote"

Epidote \Ep"i*dote\, n. [Gr. ? to give besides; ? over + ? to give: cf. F. ['e]pidote. So named from the enlargement of the base of the primary, in some of the secondary forms.] (Min.) A mineral, commonly of a yellowish green (pistachio) color, occurring granular, massive, columnar, and in monoclinic crystals. It is a silicate of alumina, lime, and oxide of iron, or manganese.

Note: The Epidote group includes ordinary epidote, zoisite or lime epidote, piedmontite or manganese epidote, allanite or cerium epidote.

n. Any of a class of mixed calcium iron aluminium sorosilicates found in metamorphic rocks.

Epidote is a calcium aluminium iron sorosilicate mineral.