Boehmite occurs in microscopic plates (orthorhombic system) as well as in pea shaped aggregates called pisolites. Diaspore, identical in chemical composition with boehmite but structured differently, occurs in emery deposits and in bauxite and laterite. It forms thin whitish, grayish, or colorless platy or elongated crystals, as well as scales and cleavable, foliated masses. Its luster is brilliant or vitreous pearly. Gibbsite forms white or gray six - sided tabular crystals (monoclinic system) with one perfect cleavage. Often the chief mineral of bauxite or laterite deposits occurs in low-temperature hydrothermal veins.