AlFe2Si4O10OH2nH2O

AlFe2Si4O10OH2nH2O is a general formula used to describe a hydrated aluminosilicate of the phyllosilicate (sheet silicate) family. In this representation, silicon and oxygen form silicate layers with the core unit Si4O10, while aluminum and iron occupy octahedral sites within or between these layers. Hydroxyl groups (OH) balance charge in the octahedral framework, and water molecules are incorporated between layers or in interlayer spaces; n denotes the variable hydration level.

As a member of the phyllosilicate class, the structure typically consists of layered sheets that can be dioctahedral or trioctahedral in composition, with cation substitutions (such as Al3+ and Fe3+/Fe2+) occurring within the octahedral sheets. The exact mineral identity depends on the distribution of aluminum and iron and on which interlayer cations or water molecules are present. The formula also allows for a range of hydration states, reflecting dehydration or hydration under different temperatures and pressures.

Occurrence and applications: Minerals with similar formulas appear in metamorphic and hydrothermal environments, often associated with other phyllosilicates. The composition can be realized in natural minerals or synthesized for industrial uses, including ceramics, refractories, catalysis, adsorption, and barrier or filler materials, where layered aluminosilicates are valued for their thermal stability and surface properties.

Notes: The formula is a simplified representation of composition and structure. Real samples may exhibit varying Fe oxidation states, cation substitutions, and interlayer cations (such as alkali or alkaline earth metals) that influence properties.

See also: phyllosilicate minerals, talc, pyrophyllite, illite, clay minerals.