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All the forms, except the prisms and basal pinacoid, are sphenoids.

All the closed forms are hexagonal bipyramids; the open forms are hexagonal prisms or the basal pinacoid.

There is an imperfect cleavage parallel to the basal pinacoid, and the fracture is conchoidal.

Acute rhombohedra in combination with the basal pinacoid are also frequent, giving crystals of octahedral aspect.

The cleavage is perfect parallel to the basal pinacoid, and less marked parallel to the prism.