Alunogen
Chemical Formula	Al2(SO4)3·17H2O
Species	Sulfates
Crystal System	Triclinic
Mohs Scale	1-2
Color	Colorless in crystals, aggregates white, or pale yellow or red from impurities.
Streak	White
Luster	Vitreous, Silky
Refractive Index	n = 1.473 n = 1.474 n = 1.480
Diaphaneity	Transparent
Crystal Habit：Crystals rare, small; prismatic or with a hexagonal outline about ; very complex, with about 60 forms noted. Commonly as delicate fibrous masses or crusts; effloresences; massive, fibrous to 5mm.
Geological Setting：Forms by reaction of sulfates from decomposing sulfides with aluminous minerals in shales and slates; in gossan or altered wall rock of pyritic deposits in arid regions; in coal seams; in relatively low-temperature fumaroles.