SiO4units

The SiO4 unit, also known as the orthosilicate tetrahedra, is the fundamental building block of silicate minerals. It consists of a central silicon atom covalently bonded to four oxygen atoms arranged at the corners of a tetrahedron. This structure, with a net charge of -4, is highly stable due to the strong bonds between silicon and oxygen. In minerals, these SiO4 units can exist in isolation, forming nesosilicates, or link together in various ways to create more complex structures.

These linking patterns include the formation of discrete pairs (sorosilicates), rings (cyclosilicates), single chains (inosilicates), double chains (inosilicates), sheets (phyllosilicates), and three-dimensional frameworks (tectosilicates). The way these tetrahedra connect influences the physical and chemical properties of the resulting minerals, such as their hardness, cleavage, and melting point. For instance, the framework structure of quartz (SiO2) makes it very hard and resistant to weathering, while the sheet structure of mica allows for easy cleavage. The SiO4 unit's ability to polymerize in diverse ways is the reason for the vast variety of silicate minerals found on Earth, which constitute over 90% of the Earth's crust.