Gedrite

General Information:
 Chemical Formula:
[ ]Mg5Al2Si6Al2O22(OH)2
 Composition:
(Molecular Weight = 783.97 gm)
Magnesium 15.50 % Mg
Aluminum 13.77 % Al
Silicon 21.49 % Si
Hydrogen 0.26 % H 
Oxygen 48.98 % O 
 Empirical Formula:
Mg5Al2(Si6Al2O22)(OH)2
 IMA Status:
Approved IMA 1978
 Locality:
Heas Valley near Gedres, France.
 Name Origin:
Named for the locality.
Physical Properties:
 Cleavage:
[210] Perfect, [100] Indistinct, [001] Indistinct
 Color:
brown, brown green, green, gray, or gray white.
 Density:
3.15 - 3.57, Average = 3.36
 Diaphaniety:
Transparent to Subopaque
 Habits:
Massive - Fibrous - Distinctly fibrous fine-grained forms., ,
 Hardness:
5.5-6 - Knife Blade-Orthoclase
 Luster:
Vitreous - Silky
 Streak:
gray white
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