sphenoid

Demonstration of basic crystal form.

Can change relative axis lengths in OpenSCAD source.

The "sphenoid" with equal axes is a tetrahedron (sphenoid_tetrahedron) which belongs to the Isometric System (e.g., cube, octahedron, dodecahedron).
With unequal axes (sphenoid_30_30 and sphenoid_30_50) the sphenoid belongs to the Tetrahedral System.