What is an octahedron in mineralogy ?

Octahedron : definition

The octahedron is a closed polyhedron composed of eight faces each having the shape of an equilateral triangle, specific to the minerals of the cubic system. In a regular octahedron, all eight faces have the same area. The figure shows the {111} shape, frequently combined with the {001} shape of the cube.

Pattern to print and cut in the section "our crystallographic models".