Based on a specimen from Thomas Range, UT

This model was inspired by a beautifully symmetric but tiny crystal of bixbyite. There are little concavities along the edges of the main crystal, as well as the expected trapezohedral corner modifications. A little investigating convinced me that the faces that made up the concave regions were also trapezohedron faces, but what were they doing in the centers of cube edges, and why were they so nicely symmetrical? And what, if anything, did they have to do with the striations that crossed in the center of every cube face?

Based on a specimen from Topaz Mountain, UT

This beautiful specimen of bixbyite on topaz was just crying out for a model! Nothing too complicated here, just a cube and trapezohedron in nicely balanced proportions. Cubes of bixbyite often have trapezohedral modifications on their corners, but often the modifying faces are tiny. This crystal has comparatively large trapezohedron faces, which makes an attractive combination of forms. The photos below are taken with the same orientation, looking down a 4-fold axis. The other photo was taken looking down a 3-fold axis, and really showcases the unique wood that makes up the trapezohedron faces.