Alaliite

Alaliite is a rare mineral species described as a hydrated aluminum silicate. It has attracted interest because of its unusual combination of aluminum-rich chemistry and layered silicate structure, which places it among the more distinctive members of the aluminosilicate group. The name honors the locality associated with the type material.

Chemistry and crystal structure are not fixed by a single formula, as the composition shows variation with hydration and trace substitutions. In general, alaliite comprises aluminum and silicon in a framework of oxygen, with hydrogen-bearing species contributing to the interlayer region. The structure is described as layered, with aluminum-centered octahedra and silicon-centered tetrahedra forming sheets that are joined by weaker interlayer bonds, giving a phyllosilicate-like character.

Occurrence and formation are linked to metamorphic and hydrothermal environments. Alaliite has been reported from low- to mid-grade metamorphic rocks and from hydrothermal pegmatites, often in association with minerals such as muscovite, albite, garnet, and zoisite. It typically occurs as small prisms or tabular grains that are dispersed within matrix rocks or occur as microcrystalline coatings on other silicate minerals.

Physical properties commonly noted for alaliite include a color range from colorless to pale yellow, a vitreous to pearly luster, and a white streak. The Mohs hardness is estimated around 5 to 6, and cleavage is described as perfect on the (001) plane in observed specimens. The mineral remains the subject of ongoing study to confirm its precise composition, crystal structure, and placement within the aluminosilicate framework.