University of Colorado

Mineral Structure Data

Epidote Group

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)      


Form.Wt.        454.36      454.36        478.6 
Z               4           2             2           2           2
CrystalSystem   Orth        Mono          Mono        Mono        Mono
PointGroup      mmm         2/m           2/m         2/m         2/m
SpaceGroup      Pnma        P21/m        P21/m        P21/m        P21/m        P21/m

UnitCell
a(Å)             16.212      8.879      8.8877      
b(Å)             5.559       5.583      5.6275
c(Å)             10.036      10.155     10.1517

beta                        115.50      115.383             

Vol(Å3)       904.47      454.36      458.73

MolarVol             136.19      136.83      138.15     
Density              3.336       3.321       3.465   

Thermal Expansion(Volumetric)
alpha         
a0  
a1 
a2 

Elastic Properties
Ks(GPa)        
G(Gpa)
Mineral Data Base Index

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