Mineral Structure Data
The Epidote group is composed of minerals of the general formula Ca2Al3Si3O12(OH). Zoisite is orthorhombic with Z = 4 whereas clinozoisite and epidote are isostructuiral monoclinic and have Z = 2. Epidote is the name give to the green variety that contains Fe3+ in substitution for AL in one of three octhedral sites. tend to Allanite is a rare earth-rich variety that a trivalent REE in one of the Ca sites and charge compensation is achieved by Fe2+ for Al. Handcockite has Pb and/or Sr substituting in one of the Ca sites.
The crystal structure of epidote .
End-Member Zoisite Clinozoisite Epidote Handcockite Allanite Formula Ca2Al3Si3O12(OH) Ca2Al3Si3O12(OH) Ca2FeAl3Si3O12(OH) Ca(Pb,Sr)FeAl3Si3O12(OH) CaRE(Fe,Al)3Si3O12(OH)
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