Grunerite
Chemical Formula	Fe7Si8O22(OH)2
Species	Silicates
Crystal System	Monoclinic
Mohs Scale	5-6
Specific Gravity	3.45
Color	Ashen, brown, brownish green, dark gray
Streak	Colorless
Luster	Vitreous
Refractive Index	n = 1.663 - 1.686 n = 1.680 - 1.709 n = 1.696 - 1.729
Diaphaneity	Translucent to opaque
Crystal Habit：Columnar