| Usually cubes, {001}; less often octahedrons, {111}; and rarely dodecahedrons{011}. Also some hexoctahedrons and tetrahexahedrons. Combinations of these forms are common, with cube corners and edges often being modified. {001} usually smooth and lustrous, {111} rough and dull. Crystals distorted at times by unequal development of faces e.g. {013}. composite from such as minute cubes aggregated to form an octahedron, 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). |
