Scalenohedron

Though the hexagonal scalenohedron is derived from the double twelve-faced pyramid, by the development of half its faces, and might be constructed from that figure, it is more readily obtained from the positive or negative rhomboid which may be supposed to be inscribed in the scalenohedron.

By bringing together the rhombohedron and the scalenohedron, as has been done in Fig. 119, it will be noticed that the lateral edges of the two forms have a similar position towards the axes, so that for every scalenohedron there must be a rhombohedron whose lateral edges coincide with the lateral edges of the other form. This rhombohedron is called the inscribed rhombohedron of the scalenohedron.

1907, Benjamin K. Emerson, Joseph H. Perry, The Green Schists and Associated Granites and Porphyries of Rhode Island, US Geological Survey, Bulletin Number 311, page 24, Other steep scalenohedrons of the principal zone are also often present, sometimes in addition to y, sometimes taking its place.

Calcite crystals show a great variety of habits — acute and obtuse rhombohedra and scalenohedra, prisms, and thin tabular forms.