Staurolite

The name of Staurolite is derived from the Greek in reference to the common twinning.  A characteristic 60 degrees cross-shape is known as Saint Andrew´s penetration twinning more rare 90 degrees cross-shape as cruciform penetration twinning. Staurolite is a typical regional metamorphic mineral of intermediate grade.


Synonyms:  Croisette, Fairy Stone
Classification:  Silicates, Nesosilicates, Staurolite Group
Chemical formula:  Fe2+2Al9Si4O23(OH)
Crystal system:  Monoclinic
Density (g/cm3):  3.74 - 3.83 measured, 3.686 calculated
Tenacity:  Brittle
Cleavage:  Distinct on {010}
Fracture:  Sub-Conchoidal
Hardness (Mohs):  7 - 7,5
Colour:  Dark brown, brownish-black, red-brown
Lustre:  Sub-Vitreous, Resinous
Streak:  White to grayish
Transparency:  Translucent

 

 

 
 
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