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Calcite cleaves in three directions parallel to the faces of the primitive rhombohedron.

Chalybite crystallizes in the rhombohedral system and is isomorphous with calcite; like this it possesses perfect cleavages parallel to the faces of the primitive rhombohedron, the angles between which are 73� 0′.

The crystals have the form of a hexagonal prism m terminated by a rhombohedron r, the alternate edges between these being sometimes replaced by the faces of a rhombohedron s.

As in the other rhombohedral carbonates, the crystals possess perfect cleavages parallel to the faces of the rhombohedron.

The end faces are cut off in such a manner that the angle of 72� which they originally form with the lateral edge of the rhombohedron is reduced to 68�.