General Information:
Chemical Formula:
(Fe++,Mg,Zn)2Al9(Si,Al)4O22(OH)2
Environment:
Metamorphosed aluminous sedimentary rocks.
Locality:
Common world wide occurrences.
Name Origin:
From the Greek, stauros - "cross" and lithos - "stone" in allusion to the common cross shaped twins of the crystals.
Physical Properties:
Cleavage:
[010] Distinct
Color:
brownish yellow, brownish black, yellow brown, dark brown, or reddish brown.
Density:
3.65 - 3.77, Average = 3.71
Diaphaniety:
Translucent to opaque
Habits:
Tabular - Form dimensions are thin in one direction., Twinning Common - Crystals are usually twinned.,
Hardness:
7-7.5
Luminescence:
Non-fluorescent.
Luster:
Vitreous - Dull
Streak:
gray
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