Staurolite
Keivy, Kola Peninsula
Russia
This specimen measures 7cm x 7cm x 1cm
Staurolite Fe2Al9Si4O22(OH)2
Nesosilicates; basic silicate or iron and aluminum, often with some magnesium and zinc
Color and Luster: Yellowish brown, reddish to brownish black, weathering to gray; vitreous, dull; streak white
Hardness: 7-7.5
Cleavage: Poor, one direction lengthwise
Fracture: Uneven to subconchoidal, brittle
Crystals: Monoclinic(pseudo-orthorhombic); in single or twinned crystals; single crystals are prismatic and show psuedohexagonal cross section; twinned crystals show two individual crystals intergrown at nearly 60°(sawhorse twin) or 90°(cross twin)
Note: Specimen aquired from Dr. Godovikov of Fresman Museum, Moscow, 1994.
Photo by Mary Sutherland
Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals