They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
[1][2][3] In mineralogy, the crystalline forms of silica (silicon dioxide, SiO2) are usually considered to be tectosilicates, and they are classified as such in the Dana system (75.1).
On Earth, a wide variety of silicate minerals occur in an even wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years.
These processes include partial melting, crystallization, fractionation, metamorphism, weathering, and diagenesis.
For example, a type of plankton known as diatoms construct their exoskeletons ("frustules") from silica extracted from seawater.
The frustules of dead diatoms are a major constituent of deep ocean sediment, and of diatomaceous earth.
[citation needed] A silicate mineral is generally an inorganic compound consisting of subunits with the formula [SiO2+n]2n−.
For example, in the mineral orthoclase [KAlSi3O8]n, the anion is a tridimensional network of tetrahedrums in which all oxygen corners are shared.