epidote group

The epidote group comprises colorless to green or yellow-green silicate minerals with the general chemical formula A₂B₃(SiO₄)(Si₂O₇)O(OH). In this formula, A is typically calcium, and B is usually aluminum, often with substitutions of other elements like manganese, cerium, or iron. Structurally, these minerals feature chains of octahedra linked by silicate groups.1

Members of the epidote group, such as epidote, clinozoisite, zoisite, piemontite, and allanite, are commonly found as secondary minerals in metamorphosed rocks. Their presence can indicate the intensity of metamorphic conditions. These minerals can also form during the metamorphism of igneous rocks or through the hydrothermal alteration of feldspar. The epidote-amphibolite facies, a classification of metamorphic rocks, forms under moderate temperature and pressure and is characterized by minerals including epidote, biotite, and amphibole.12