Al2Si5O13OH2

Al2Si5O13OH2 is a chemical formula representing a hydrated aluminosilicate composition containing aluminum, silicon, oxygen, and hydroxide groups. In some representations it is written as Al2Si5O13(OH)2, highlighting the presence of two hydroxyl (OH) groups in the structural unit. The formula places aluminum and silicon in a tetrahedral framework with oxygen, a common feature of aluminosilicate minerals and synthetic silicate materials.

In aluminosilicate frameworks, silicon and aluminum typically occupy tetrahedral sites linked by shared oxygen atoms. Substitution of silicon by aluminum introduces negative framework charge, which in natural minerals is balanced by extra cations (such as Na+, K+, Ca2+) or by hydroxyl groups and water molecules in interlayer or defect sites. The presence of OH groups in the formula indicates termination of the framework or incorporation of hydroxyls within the structure, a characteristic common to many clays, zeolites, and layered silicates.

The exact mineralogical identity of a compound with this precise formula can be context-dependent. It may describe a theoretical or synthetic aluminosilicate fragment, a component of a larger mineral structure, or a unit within a zeolite or clay-like phase. As such, Al2Si5O13OH2 is more often encountered in discussions of aluminosilicate chemistry and materials science than as a standalone natural mineral name.

See also: Aluminosilicate, Silicate minerals, Zeolites, Clays.