Fe3Al2Si4O10OH2

Fe3Al2Si4O10(OH)2 is a chemical formula that describes a hydrous aluminosilicate with a pyrophyllite-like framework. In mineralogical terms, it would represent a ferrian end-member of the pyrophyllite group, where iron and aluminum occupy octahedral sites in a dioctahedral phyllosilicate structure paired with a silicate tetrahedral sheet of Si4O10(OH)2.

Composition and structure

The formula indicates three iron cations and two aluminum cations per formula unit combined with four silicon, ten oxygens, and two hydroxyl groups. The structure would be based on a sheet silicate (phyllosilicate) arrangement in which SiO4 tetrahedra form a continuous layer that is linked to an octahedral sheet containing Fe and Al. This arrangement is characteristic of pyrophyllite and related minerals, which typically exhibit low hardness and perfect basal cleavage.

Relation to pyrophyllite

Pyrophyllite itself has the end-member formula Al2Si4O10(OH)2. Substituting iron for aluminum in the octahedral sheet yields ferrian analogues, of which Fe3Al2Si4O10(OH)2 would be one theoretical example. In natural samples, complete adherence to an exact Fe3Al2 composition is uncommon; variations with different Fe/Mg/Al ratios are more typical.

Occurrence and classification

If a mineral with this exact composition were discovered, it would be described within the pyrophyllite family or as a ferrian pyrophyllite variant, depending on crystallography and cation ordering. Pyrophyllite-group minerals form in metamorphic rocks and hydrothermal environments, and iron-rich variants would reflect local chemical conditions.

See also

Pyrophyllite, phyllosilicates, clay minerals, ferripyrophyllite (conceptual end-members).