Recommended nomenclature of epidote-group minerals

Abstract

Epidote-group minerals are monoclinic in symmetry and have topology consistent with space group P2 1 /m and the general formula A 2 M 3 [T 2 O 7 ][TO 4 ](O,F)(OH,O). Zoisite is an orthorhombic polymorph of clinozoisite Ca 2 Al 3 [Si 2 O 7 ][SiO 4 ]O(OH) and is thus not considered a member of the epidote-group. Epidote-group minerals are divided into three subgroups. (1) Members of the clinozoisite subgroup are derived from the mineral clinozoisite Ca 2 Al 3 [Si 2 O 7 ][SiO 4 ]O(OH) by homovalent substitutions only. The key cation-and anion-sites are A1