Striated cube of Pyrite (pyritohedral symmetry)3D ModelNoAI
If the pyritohedral type of symmetry be applied to planes each parallel to two of the axes, it is seen that this symmetry calls for six of these, and the resulting form is obviously a cube. This cube cannot be distinguished geometrically from the cube of the normal class (m-3m), but it has its own characteristic molecular symmetry.
The true symmetry may sometimes be shown by natural markings on crystal faces. This is often the case with Pyrite (class m-3), where cubes of the mineral may have striated faces, produced by the incipient development of planes other than {100} (i.e. pyritohedral/pentagon-dodecahedron faces {210}). The run of the striations enables the faces to be grouped into three pairs of opposites, and hence indicates that the principal axes have two-fold, not four-fold symmetry.
Natural pyritohedron: https://skfb.ly/6XRBU
Website: http://geology.uaic.ro/muzee/mineralogie/
Concept & 3D-modelling by dr. Andrei Ionut APOPEI
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