sorosilicate

Sorosilicate, also known as disilicate, is a class of silicate minerals characterized by silicate tetrahedra linked in pairs through a single shared oxygen, forming Si2O7 groups. The fundamental structural unit is the disilicate group, consisting of two SiO4 tetrahedra that share one corner oxygen. This arrangement yields a discrete Si2O7 unit that is balanced by surrounding cations in the mineral.

In silicate mineral classification, sorosilicates occupy a distinct category between nesosilicates (isolated SiO4 tetrahedra) and more polymerized silicate groups such as chains, rings, sheets, and frameworks. The presence of Si2O7 units is a diagnostic feature of this group, although the exact structure and degree of polymerization can vary with different minerals and substitutions.

Formation and occurrence: Sorosilicates form in metamorphic and hydrothermal environments, especially in rocks that supply calcium, aluminum, and other metals. They are commonly stable under moderate metamorphic conditions and can appear as alteration products in contact metamorphism or within complex metamorphic assemblages.

Examples: The epidote group minerals are classic sorosilicates, including epidote and zoisite. Other sorosilicate minerals occur in metamorphic rocks and hydrothermal veins, often associated with calcium- and aluminum-rich phases.

Physical properties: Sorosilicate minerals typically exhibit a range of colors and commonly have a vitreous to resinous luster. Crystal habits vary; many form prismatic or tabular crystals, reflecting their diverse crystal structures and compositions.