ferrisilicate

Ferrisilicate is a general, non-systematic term used to describe compounds that contain both iron and silicate components. It is not the name of a distinct mineral species, but a descriptive label in petrology and mineralogy for iron-rich silicate materials whose chemical formula reflects Fe and Si–O networks. In practice, ferrisilicate can refer to iron-bearing silicate minerals and to natural or synthetic glasses with silicate frameworks in which iron is a major constituent.

Within the silicate mineral groups, iron-rich end-members such as fayalite (Fe2SiO4) in the olivine family and ferrosilite (FeSiO3) in the pyroxene family are typical examples of ferrisilicates. Iron can substitute for magnesium in many silicate structures, leading to a range of solid-solution series from forsterite–fayalite (Mg2SiO4–Fe2SiO4) and enstatite–ferrosilite (MgSiO3–FeSiO3).

Occurrence and formation: Ferrisilicates form in igneous rocks as differentiation proceeds, in metamorphic rocks under high-grade conditions, and in hydrothermal systems where iron-rich fluids interact with silicate minerals. They are common in mafic to ultramafic rocks and can occur as primary minerals or as alteration products.

Notes: The term should not be confused with ferrosilicon, an iron–silicon alloy used in steelmaking. In formal mineral nomenclature, specific names such as fayalite or ferrosilite are preferred over the umbrella term ferrisilicate.