nesosilikáty

Nesosilikáty, also known as orthosilicates, are a subclass of silicate minerals. Their defining characteristic is the presence of isolated [SiO4]4- tetrahedra, where a central silicon atom is bonded to four oxygen atoms. These tetrahedra are not linked to each other by sharing oxygen atoms, meaning they exist as discrete units.

In the crystal structure of nesosilikáty, these [SiO4]4- tetrahedra are held together by interstitial cations, typically divalent or trivalent metal ions such as Mg2+, Fe2+, Fe3+, Al3+, Ca2+, and Mn2+. The size and charge of these cations play a crucial role in determining the specific mineral species formed and the overall structure. Common coordination numbers for these cations with oxygen are 4, 6, or 8.

Examples of nesosilikáty include olivine, which forms a solid solution series between forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Other important nesosilikáty include garnets (a group of minerals with the general formula X3Y2(SiO4)3), staurolite, and zircon. These minerals are often found in igneous and metamorphic rocks and can be important gemstones, such as peridot (gem-quality olivine) and garnet. Their relative structural simplicity and the presence of various cations contribute to a wide range of physical properties, including hardness, color, and density.