1. Four sided polyhedron; all sides are equidimensional and triangular shaped. Minerals shaped as tetrahedrons belong to the isometric system. 2. The building block of all silicates. It is composed of one silicon atom equidimensionally placed around four oxygen atoms. The groups of silicates are classified based on how the tetrahedrons join together.
A tetrahedron (plural: tetrahedra) is a polyhedron composed of four triangular faces, three of which meet at each vertex. A regular tetrahedron is one in which the four triangles are regular, or "equilateral," and is one of the Platonic solids.