Offretite

General Information:
 Chemical Formula:
(K2,Ca)5Al10Si26O72·30(H2O)
 Environment:
Alteration of basalt with the addition of potash.
 IMA Status:
Approved IMA 1962
 Locality:
Mont Simiouse, near Montbrison, Loire, France.
Physical Properties:
 Cleavage:
[0001] Distinct
 Color:
colorless or white.
 Density:
2.13
 Diaphaniety:
Transparent to Translucent
 Hardness:
4-4.5 - Between Fluorite and Apatite
 Luster:
Vitreous (Glassy)
 Streak:
white
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