The Epidotgruppe is a group of silicate - minerals with the same crystal structure and monoclinic symmetry. The minerals of the epidote group have the general chemical composition A 2 M 3 [T 2 O 7 ] [TO 4 ] (O, F) (OH, O), where A stands for divalent , M for trivalent and T for tetravalent cations . However, they can also contain ions of a different valence through substitution . The most important chemical components are Ca , REE , Al , Fe and Si . The orthorhombic zoisite is a polymorph (that is, it has the same chemical composition but different crystal structure) and does not belong to the epidote group.
The minerals of the epidote group
Based on chemical differences, the epidote group can be divided into three subgroups. The following minerals are included in the epidote group by the International Mineralogical Association (IMA), outdated names are shown in italics:
- Clinozoisite subgroup
- Clinozoisite , clinozoisite (Sr) ( niigataite ), clinozoisite (Pb)
- Epidote , Epidote- (Pb) ( Hancockit ), Epidote- (Sr), Ferriepidot, Ferriepidot- (Sr), Ferriepidot- (Pb), Vanadoepidot, Vanadoepidot- (Sr), Vanadoepidot- (Pb)
- Mukhinit , Mukhinit- (Sr), Mukhinit- (Pb)
- Tawmawit , Chromotawmawit
- Piedmontite , Piemontite- (Sr) ( Strontiopiemontite ), Piemontite- (Pb), Manganipiemontite, Tweddillit ( Manganipiemontit- (Sr) )
- Allanite subgroup
- Allanite - (Ce), - (La), - (Nd), - (Y), ferricallanite (Ce), vanadoallanite (SEE), chromoallanite (SEE)
- Dissakisit- (Ce), - (La), Ferridissakisit- (SEE), Vanadodissakisit- (SEE), Manganidissakisit- (SEE), Chromodissakisit- (SEE)
- Androsite - (SEE), Manganiandrosite- (La), - (Ce), Ferriandrosite- (SEE), Vanadoandrosite- (Ce), Chromoandrosite- (SEE)
- Dollaseit subgroup
Education and Locations
The minerals of the epidote group are formed by numerous igneous and metamorphic processes in a wide variety of geological situations. For this reason there are numerous sites around the world, although some of the rare earth members in particular are extremely rare.
All minerals of the epidote group have the monoclinic symmetry and the crystallographic space group P2 1 / m in common.
- T. Armbruster, P. Bonazzi, M. Akasaka, V. Bermanec, C. Chopin, R. Gieré, S. Heuss-Assbichler, A. Liebscher, S. Menchetti, Y. Pan and M. Pasero: Recommended nomenclature of epidote -group minerals . European Journal of Mineralogy 18 (2006), pages 551-567.