Andalusite
Chemical Formula	Al2SiO5
Species	Silicates
Crystal System	Orthorhombic
Mohs Scale	6-7
Specific Gravity	3.17
Color	Pink, Purple, yellow, green, white, gray; in thin section, colorless to pink or green
Streak	White
Luster	Vitreous, Sub-Vitreous, Greasy
Refractive Index	n = 1.629 - 1.640 n = 1.633 - 1.644 n = 1.638 - 1.650
Diaphaneity	Transparent, Translucent
Cleavage	Distinct/GoodGood on Poor on
Fracture	Irregular/Uneven, Sub-Conchoidal
Crystal Habit：As euhedral crystals or columnar aggregates having nearly square cross sections; fibrous compact to massive
Geological Setting：A result of contact metamorphism of argillaceous sediments, also in regionally metamorphosed schists. Rare in granites and pegmatites, which however afford the largest crystals. Detrital in some sandstones.