Fe2Al9Si4O22(OH)2Monoclinic
Staurolite
Fe2Al9Si4O22(OH)2
SilicatesChemical FormulaFe2Al9Si4O22(OH)2
Crystal SystemMonoclinic
Mohs Hardness7
Specific Gravity3.75
ColorRed brown to brownish black
LusterResinous to vitreous
StreakWhite to grayish
CleavageOne direction
FractureSubconchoidal
Occurrence
Found in metamorphic rocks. Forms characteristic cross-shaped twins.