Usually cubes, {001}; less often octahedrons, {111}; rarely dodecahedrons{011}. Also some hexoctahedrons and tetrahexahedrons. Combinations of these forms common, cube corners and edges are often modified. {001} usually smooth and lustrous, {111} rough and dull. Crystals distorted at times by unequal development of faces, as of {013}. Often markedly composite; minute cubes aggregated to form an octahedron at times, or as an overgrowth of crystals upon the corners of an earlier formed crystal of differing habit. Massive; compact; earthy, columnar (rare), or in globular aggregates; botryoidal (rare)