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 n? = 1.644 - 1.648, n? = 1.654 - 1.657 and n? = 1.661 - 1.668.

Boehmite occurs in tropical laterites and bauxites developed on alumino-silicate