Kyanite
Fazenda do Congonas, Minas Gerais, Brazil
The specimen shown is from Fazenda do Congonas, Minas Gerais, Brazil. The longest crystal measures 44 cm. in length. The specimen was acquired in 1985 from Ann Pizzorusso.
Kyanite Al2SiO5
Nesosilicates; Aluminum silicate
Color and Luster: Blue, white, colorless, gray, green, nearly black; vitreous; streak colorless
Hardness: Varies: lengthwise 4-5, crosswise 6-7
Cleavage: Perfect, one direction lengthwise; good in a second direction
Fracture: Splintery; transparent to translucent
Crystals: Triclinic; usually in bladed crystal aggregates, less often in terminated crystals
Kyanite is a common rock forming mineral that shares the same chemical composition with it's two polymorphs silimanite and andalusite. It is the high pressure, triclinic member of the alumino- silicate polymorphs. Kyanite is used in the manufacturing of high temperature, acid resistant ceramics and electrical insulators.
Photo by Lance Kearns
Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals