Atomic Positional Parameters

Na 0.1778 0.1778 0.1778
Cl 0.0000 0.0000 0.0000
Si 0.2500 0.5000 0.0000
Al 0.2500 0.0000 0.5000
O  0.1390 0.1494 0.4383

Reference
Hassan I and Grundy HD (1984) Acta Cryst., B 40, 6-13.

Mineral Chemistry
Sodalite has an aluminosilicate framework with SiO₄ and AlO₄ tetrahedra present in approximately equal numbers. Rings of these tetrahedra, which may be four-fold or six-fold, form channels which accommodate sodium and chloride ions. Sodium ions surround chloride ions in a tetrahedral arrangement. Sodalite is a member of the feldspathoid group of minerals, anhydrous framework silicates richer in cations than feldspars; feldspathoids crystallise from melts which are deficient in silica.

Substitution of chloride ions in sodalite with half the number of sulphate ions gives the mineral composition of nosean (Na₈[Al₆Si₆O₂₄]SO₄), while replacement of chloride with sulphate and partial replacement of sodium with calcium gives haüyne ((Na,Ca)_4-8[Al₆Si₆O₂₄](SO₄)_1-2).

Lazurite, a sodalite-structured mineral, is the dominant phase in lapis-lazuli. This mineral has chlorine replaced by sulphur as both sulphide and sulphate anions; the cation sites are occupied by both calcium and sodium.

The sodalite 'cage', part of the aluminosilicate framework, forms a structural element which is common to many synthetic zeolite phases.

view sodalite 'cage' in whole frame

The CHIME figure of sodalite shows chlorine ions as large green spheres, oxygens as small red spheres, and sodiums as yellow spheres. The tetrahedron of sodiums surrounding chlorines may be observed by inspecting the central chloride ion. Aluminiums and silicons are at the centre of tetrahedra of oxygens. The unit cell is outlined.