Sodalite is a member of the Feldspathoid group of the Tectosilicates. It has a composition of Na8Si6Al6O24Cl2 and is in the isometric crystal class. The structure of sodalite is interesting in that it is a silicate that contains a large accessory anion, in this case, chlorine. The silica tetrahedral backbone structure is such that it produces large cage-like cavities in which the Cl is housed.
Highlighting FeaturesSodium (Na) atoms Silicon (Si) atoms Aluminum (Al) atoms Oxygen (O) atoms Chlorine (Cl) atoms Single unit cell All atoms
Sodalite seldom occurs as individual crystals; usually massive in formation. Transparent crystals have been found in the lavas of Vesuvius. The massive blue variety is found in Maine, USA, and in Ontario and British Columbia, Canada. The blue variety is sometimes used as a semi-precious stone.
Lons J., and H. Schulz H. 1967. Acta Cryst., 23:434-436