Sodalite (/ˈsoʊ.dəˌlaɪt/ SOH-də-lyte) is a tectosilicate mineral with the formula Na8(Al6Si6O24)Cl2, with royal blue varieties widely used as an ornamental gemstone.

The three silicon atoms and the three aluminum atoms listed above closest to a given corner of the unit cell form a six-membered ring of tetrahedra, and the four in any face of the unit cell form a four-membered ring of tetrahedra.

A discontinuity of the thermal expansion coefficient occurs at a certain temperature when chloride is replaced by sulfate or iodide, and this is thought to happen when the framework becomes fully expanded or when the cation (sodium in natural sodalite) reaches the coordinates

Natural sodalite holds primarily chloride anions in the cages, but they can be substituted by other anions such as sulfate, sulfide, hydroxide, trisulfur with other minerals in the sodalite group representing end member compositions.

[12] A light, relatively hard yet fragile mineral, sodalite is named after its sodium content; in mineralogy it may be classed as a feldspathoid.

Well known for its blue color, sodalite may also be grey, yellow, green, or pink and is often mottled with white veins or patches.

[14] When hackmanite from Mont Saint-Hilaire (Quebec) or Ilímaussaq (Greenland) is freshly quarried, it is generally pale to deep violet but the color fades quickly to greyish or greenish white.

Conversely, hackmanite from Afghanistan and the Myanmar Republic starts off creamy white but develops a violet to pink-red color in sunlight.

Sodalite was first described in 1811 for the occurrence in its type locality in the Ilimaussaq complex, Narsaq, West Greenland.

[2] Occurring typically in massive form, sodalite is found as vein fillings in plutonic igneous rocks such as nepheline syenites.

Other associated minerals include nepheline, titanian andradite, aegirine, microcline, sanidine, albite, calcite, fluorite, ankerite and baryte.

[4] Significant deposits of fine material are restricted to but a few locales: Bancroft, Ontario (Princess Sodalite Mine), and Mont-Saint-Hilaire, Quebec, in Canada; and Litchfield, Maine, and Magnet Cove, Arkansas, in the US.

The Ice River complex, near Golden, British Columbia, contains sodalite.

[15] Smaller deposits are found in South America (Brazil and Bolivia), Portugal, Romania, Burma and Russia.

Euhedral, transparent crystals are found in northern Namibia and in the lavas of Vesuvius, Italy.

[17] The mesoporous cage structure of sodalite makes it useful as a container material for many anions.