A silicate consisting of planar layers of octahedra bound to tetrahedra above and below with a characteristic repeat distance between t-o-t layers. They are the primary component of soils and are excellent trappers of water, which is held between layers. The layer silicates are divided into the 7 Å layer silicates, 10 Å layer silicates, and chlorites based on their repeat distances. Minerals within these groups are further divided into dioctahedral and trioctahedral (Klein and Hurlbut 1985).

7 Å layer silicates include kaolinite Al₄(Si₄O₁₀)(OH)₈ (which is dioctahedral) and serpentine Mg₆(Si₄O_{10[sub])(OH)[sub]8} (which is trioctahedral). 10 Å layer silicates usually form as weathering products, and almost never as crystals. The class of 10 Å layer silicates exhibiting perfect planar cleavage is known as the micas. The group also includes the clay minerals. Chlorites include the di- and trioctahedral Mg₅Al(AlSi₃O₁₀)(OH)₈.