A silica tetrahedron is the basic unit of silicates, which are minerals in the Earth's rocks. The tetrahedron comprises a single positively charged silicon molecule surrounded by four negatively charged oxygen molecules. These structures are formed by covalent bonding, where molecules are connected by shared electrons.
Olivine, pyroxene, amphibole and quartz are all examples of silicates. The silica tetrahedra that make up each of these, however, appear in different arrangements depending on the mineral. The tetrahedra of pyroxenes form into singles chains, while amphiboles combine in double chains. Micas consist of tetrahedra combining into sheet formations. Quartz and feldspar, the most prevalent silicates, come together in complex frameworks in which every corner of each tetrahedra is shared with another.