Boehmite

Chemical Formula : AlO(OH)
Hardness : 6.5-7
Cleavage : One; rarely visible
Luster : Dull
Color : White
Streak : White
Density : 3.0
Diagnostic Features and Trivia : Boehmite almost never occurs alone, and is a primary constituent of the matrix in Bauxite.
Crystal System and Habit : Orthorhombic
Twinning : None
Polymorphs : Diaspore
Index of Refraction : alpha=1.64-1.65; beta=1.65-1.66; gamma=1.65-1.67