rhombohedral

In composition it differs entirely from sapphire, or the rhombohedral corundum.

The crystals belong to the hexagonal system, and are generally of rhombohedral habit, sometimes twinned.

The habit of the crystals may be rhombohedral, pyramidal or tabular, rarely prismatic.

Haematite crystallizes in the rhombohedral system, and is isomorphous with corundum (Al2O3).

There are two divisions of the hexagonal system; the hexagonal system properly so-called, and its rhombohedral division.