SiO4tetraedrat

SiO4 tetrahedron refers to the silicate tetrahedron, a chemical unit consisting of a silicon atom at the center of a tetrahedron formed by four oxygen atoms. In this arrangement, silicon is in the Si4+ oxidation state and each oxygen is -2, giving the SiO4 unit an overall -4 charge that is balanced in minerals by cations such as Na+, Ca2+, Mg2+, or Al3+. The geometry is a nearly ideal tetrahedron with Si–O bond lengths of about 1.60 Å and O–Si–O angles near 109.5 degrees.

Attachment to form silicate minerals occurs by sharing oxygen corners between tetrahedra. When tetrahedra share no corners, they form nesosilicates (isolated SiO4 units, e.g., olivine). Single chains (inosilicates) share two corners; double chains (amphiboles) share two in a staggered fashion; sheets (phyllosilicates) share three; frameworks (tectosilicates) share all four, yielding structures such as quartz and feldspars.

The SiO4 tetrahedron is the fundamental building block of almost all silicate minerals. Variations in connectivity, coupled with substitution at the tetrahedral or interstitial sites, produce the wide diversity of silicate mineral structures. Silicon can be partly substituted by aluminum, requiring additional charge-balancing cations and leading to substitutions in mineral compositions.

In crystallography and mineralogy, the tetrahedron is described as a [SiO4]4− unit embedded in the crystal lattice. Its properties and polymerization state influence physical properties such as hardness, cleavage, and melting behavior of silicate rocks.