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).
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. The time in our computers and clocks is kept by a silicate mineral.
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 tetrahedra to form minerals. The six most common positively-charged elements in the crust of the Earth that combine with the silica tetrahedra are (in order of most abundant to least abundant): aluminum (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.