A polymorph of hydrous aluminum oxide, alpha-AlO(OH), and isostructural with goethite, alpha-FeO(OH). The structure is comprised of double chains of edge-sharing octahedra of AlO3(OH)3along the c axis, and the chains are offset along the b axis. Diaspore occurs with corundum, often in chlorite schists and in dolomite, and as a major constituent as fine-grained matrix in bauxite.