General Information:
Chemical Formula:[ ]Ca2(Fe++3AlFe+++)Si6Al2O22(OH)
Composition:(Molecular Weight = 939.00 gm)Calcium 8.54 %
CaAluminum 8.62 %
AlIron 23.79 %
FeSilicon 17.95 %
SiHydrogen 0.21 %
H Oxygen 40.89 %
O Empirical Formula: Ca2Fe2+3AlFe3+(Si6Al2O22)(OH)2
IMA Status:Approved IMA 1978 (Dana # Added)
Name Origin:Named for its composition and for Gustav Tschermak von Sessenegg (1836-1927), Austrian mineralogist.
Physical Properties: Cleavage:[110] Perfect
Color:green, dark green, or black.
Density:3.41
Diaphaniety:Translucent to Subopaque
Hardness:5-6 - Between Apatite and Orthoclase
Luster:Vitreous (Glassy)
Streak:greenish gray
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