Diaspore, mineral, aluminum oxide AlO(OH), intermediate in composition between bauxite and corundum. Diaspore has a hardness of 6.5 to 7 and a specific gravity of 3.4. It crystallizes in the orthorhombic system (see Crystal). It is transparent or translucent, white or gray in color, sometimes with a yellowish, greenish, or brownish cast. It is frequently a product of the decomposition of corundum, emery, and bauxite and is sufficiently common to be classified as a minor ore of aluminum.