MgFeSi2O5OH2

MgFeSi2O5OH2 is a chemical formula describing a hydrous magnesium–iron silicate. In mineralogical terms, it represents a composition that can occur within phyllosilicate minerals, where silicate sheets are linked with hydroxyl groups and balanced by magnesium and iron in octahedral sites. The formula is often treated as an empirical or idealized composition rather than as a discrete mineral species.

Structurally, the silicate tetrahedra form layered sheets characteristic of phyllosilicates. The Si2O5(OH)2 repeating unit indicates a condensed tetrahedral framework with two hydroxyl groups per formula unit, while magnesium and iron occupy adjacent octahedral positions. The exact arrangement and cation distribution can vary, giving rise to a solid-solution series across Mg-rich and Fe-rich compositions.

Occurrence and associations are tied to metamorphic and hydrothermal environments where hydrated silicates form. Compositions close to MgFeSi2O5(OH)2 may be encountered in serpentinite-derived rocks and related alteration assemblages, potentially alongside serpentine minerals, chlorite, talc, and mica-group minerals. Because the formula describes a range of possible minerals rather than a single named species, exact mineralogical identification relies on methods such as X-ray diffraction and electron microprobe analysis.

Properties of minerals with this composition depend on the specific phase and its degree of hydration. Generally, hydrous phyllosilicates display softness relative to many framework silicates, variable luster, and dehydration behavior upon heating. The Mg/Fe ratio influences color and some physical characteristics within the allowed solid solution.

See also: serpentine group, smectites, phyllosilicates, hydrous silicates.