Boehmite or
böhmite is an
aluminium oxide hydroxide (γ-AlO(OH)) mineral, a component of the aluminium ore
bauxite. It is dimorphous with
diaspore. It crystallizes in the
orthorhombic dipyramidal system and is typically massive in habit. It is white with tints of yellow, green, brown or red due to impurities. It has a vitreous to pearly luster, a
Mohs hardness of 3 to 3.5 and a
specific gravity of 3.00 to 3.07. It is colorless in thin section, optically biaxial positive with
refractive indices of nα = 1.644 - 1.648, nβ = 1.654 - 1.657 and nγ = 1.661 - 1.668.