Bixbyite - cube and trapezohedron
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.
Bixbyite Model
Bixbyite on topaz
I’ve never been able to find another piece of wood like the one I used for the trapezohedron faces. I only got enough to use in two models. Now it’s used up, and I don’t know if I’ll ever be able to find another piece of wood like it.
Something that surprised me as I was writing this page is the fact that bixbyite crystalizes in the diploidal class of the isometric system, the same class as pyrite. I always assumed it was hexoctahedral, likely because bixbyite crystals generally do not exhibit lower symmetry forms like pyritohedra or diploids. Cubes, octahedra, and trapezohedra are common in bixbyite. All of these forms are also found, and are more familiar in, the full-symmetry hexoctrahedral class represented by familiar minerals like garnet, galena, and fluorite.
So if you click the “Isometric - Diploidal” tag at the bottom of this page, you will find a lot of examples of pyrite crystals, most of which have obvious lower symmetry. If you like the look of the higher symmetry forms, you might want to look at some of my garnet models, or this fluorite (link to come).
If you’re curious about the faint lines visible on the trapezohedron face just above the front cube face, or if you are a fan of bixbyite, make sure to check out my model of bixbyite with braunite lamellae.
Model details: 7" across tips. Cube faces are bubinga. Trapezohedron faces are spalted red oak.
Specimen details: Bixbyite crystal on topaz. Topaz Mountain, Thomas Range, Juab Co., Utah. 1.5 cm crystal.