Hexaoctahedron

The writer has seen a remarkably fine specimen of alluvial (Ballaarat) gold, it was a group of inch and half-inch crystals of the hexaoctahedron crystallographic form, hollowing towards the centre of the faces stair fashion, parallel to the combination lines.

Diamond, C. I. In octahedrons, hexaoctahedrons; cleavage octahedral.

The natural crystalline form of diamonds is a regular octahedron although a few have been found that were hexaoctahedrons.[…]Hexaoctahedrons have forty-eight faces.

The seven kinds consist of three unique forms which are the cube, octahedron, and rhombic dodecahedron, and four families of forms having the shape of icositetrahedra, trisoctahedra, tetrahexahedra, and hexaoctahedra.

It usually forms rounded octahedra, often twinned, transparent, yellow, brown, green, less often blue and black; it rarely occurs in the form of hexaoctahedra.