The most important and abundant group of rock-forming minerals, which can be classified according to the structural arrangement of the fundamental SiO₄ tetrahedra which are the main building blocks of the group. (a) Nesosilicates have independent SiO₄ tetrahedra linked by cations, e.g. olivine group. (b) Sorosilicates have two SiO₄ tetrahedra sharing one oxygen, e.g. epidote group. (c) Cyclosilicates have rings of three, four, or six linked SiO₄ tetrahedra, e.g. axinite and tourmaline. (d) Inosilicates (chain silicates) have SiO₄ tetrahedra linked either into single chains by sharing two oxygens, e.g. pyroxene group, or into double chains (band silicates) by alternately sharing two or three oxygens, e.g. amphibole group, (e) Phyllosilicates (sheet silicates) share three oxygens to form a flat sheet, e.g. mica group. (f) Tectosilicates have SiO₄ tetrahedra linked into a three-dimensional framework by sharing all the oxygens, e.g. feldspar and quartz groups.