A group of rock-forming minerals that make up the bulk of the earth’s outer crust (about 90%) and constitute one-third of all minerals. All silicate minerals are based on a fundamental structural unit – the SiO4 tetrahedron (see silicate). They consist of a metal (e.g. calcium, magnesium, aluminium) combined with silicon and oxygen. The silicate minerals are classified on a structural basis according to how the tetrahedra are linked together. The six groups are: nesosilicates (e.g. olivine and garnet); sorosilicates (e.g. hemimorphite); cyclosilicates (e.g. axinite, beryl, and tourmaline); inosilicates (e.g. amphiboles and pyroxenes); phyllosilicates (e.g. micas, clay minerals, and talc); and tektosilicates (e.g. feldspars and feldspathoids). Many silicate minerals are of economic importance. Pauling’s rules provide a useful guide for understanding the structures of silicates.
Silicate minerals