n.
Any of a group of colourless to green or yellow-green silicate minerals with the general chemical formula A 2 B 3 (SiO 4 )(Si 2 O 7 )O(OH), in which A is usually calcium (Ca) and B is generally aluminum (Al), although other elements are sometimes substituted.
The epidote minerals occur as reaction products of other (earlier) minerals in low-grade (formed under relatively low-temperature, low-pressure conditions), regionally metamorphosed rocks, where their occurrence is used as an indicator of metamorphic grade.