268-402 Silicates

The silicate mineral class is considered to be the most important of all the mineral classes. About 25% of the known minerals and nearly 40% of the common ones are silicates. Nearly 90% of the igneous rock-forming minerals are silicates; which means that they make up over 90% of the Earth's crust (oxides are the other dominant mineral group). Igneous rock is formed by the cooling and solidifying of lava or molten rock.

Each assemblage of silicate minerals tells us something of the environment in which it was formed. The soil in which we grow our food is made up largely of silicates. Bricks, stones, concrete, and glass are either silicates or derived from silicates. Silicates can conduct electricity and are used in a wide variety of computer technology.

The fundamental unit on which the structure of all silicates is based consists of four oxygen ions surrounding a silicon ion. This is known as the silicon-oxygen tetrahedron (SiO4). When the silicon and oxygen atoms combine, there is a net -4 charge to the molecule. This allows other positively-charged atoms to combine with the silica to form minerals. The six most common positively-charged elements in the crust of the Earth that combine with the silica are (in order of most abundant to least abundant): aluminium (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg). In some minerals, the silica tetrahedron may join with other silica tetrahedra to form various silicate structures.

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