A mineral of the feldspathoid group, crystallising in the isometric system, with chemical composition Na₄Al₃Si₃O₁₂Cl. Its tektosilicate framework, in which half the tetrahedrally coordinated Si atoms are replaced by Al, is arranged in four- and six-membered rings. The rings define sets of channels which intersect to form cavities. Na atoms reside in the channels and Cl in the cavities. Crystals are rare, usually dodecahedrons. Sodalite is usually massive or granular with poor cleavage. The Mohs hardness is 5.5–6.0, and the density 2.3. The lustre is vitreous, and the colour is usually blue but may also be white, gray, or green.