Describe the silica tetrahedron

This fundamental structural unit consists of a silicon cation surrounded by four oxygen anions giving it four negative charges. It is found in all silicate minerals (ie. amphibole, olivine, pyroxene, quartz, feldspar, etc.). The silica tetrahedra may be arranged in chains (ex: pyroxenes), double chains (ex. amphiboles), sheets (ex: micas), and frameworks (ex: quartz, feldspars), forming the basic structure of the planet.