KAlSi3O8H2O

KAlSi3O8H2O is a chemical formula that denotes a hydrated potassium aluminum silicate. The formula expands the well-known feldspar composition KAlSi3O8 by including a water molecule, indicating hydration of the feldspar framework. There is no widely accepted mineral species with the exact formula KAlSi3O8H2O in major mineral databases, so in practice the term is used in theoretical or laboratory contexts as a descriptive placeholder rather than a distinct, independently named mineral.

Chemically, KAlSi3O8 corresponds to orthoclase/sanidine-type feldspars, with a framework of linked SiO4 and AlO4 tetrahedra balanced by K+ interstitial sites. The addition of H2O in the formula suggests interstitial or bound water within the crystal structure, potentially occupying channels or coordinating with cations. In real systems, hydration of feldspar is not typically observed as a stable discrete solid; instead, alteration commonly proceeds to hydrous clay minerals such as illite, smectite, or kaolinite, often with exchange of K+.

Formation and stability of a discrete KAlSi3O8·H2O phase would depend on pressure, temperature, and chemical environment. Under hydrothermal or weathering conditions, potassium-rich feldspars tend to weather and alter rather than persist as a hydrated feldspar exact hydrate.

See also: orthoclase (KAlSi3O8), sanidine, feldspar hydration, illite, clay minerals, aluminosilicates.