Al2SiO5Triclinic
Sillimanite
Al2SiO5
SilicatesChemical FormulaAl2SiO5
Crystal SystemTriclinic
Mohs Hardness7
Specific Gravity3.68
ColorBlue, white, gray
LusterVitreous
StreakWhite
CleavageOne direction
FractureSplintery
Occurrence
Aluminum silicate polymorph. Important indicator of metamorphic conditions.