What is Sodalite?
Sodalite is a rich blue sodium aluminium silicate, widely used as an ornamental stone and valued by collectors for white veining and saturated colour.
Mineralogy and crystal structure
Reference formula: Na8(Al6Si6O24)Cl2. Sodalite has a cubic framework containing sodium, chlorine and open structural sites. Lapis-lazuli may contain sodalite but is a rock aggregate, not a synonym for pure sodalite. Sodalite is classified with silicates and has a cubic crystal system. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 2.1–2.4.
Colour, lustre and habit
Typical colours include blue, royal blue, white, grey, pink. The usual massive, granular, dodecahedral habit and vitreous, greasy lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Sodalite forms in or is associated with alkaline igneous rocks, nepheline syenites, volcanic cavities and contact zones. Important documented localities include Canada, Brazil, Namibia, Russia, Afghanistan and Greenland.
Blue architectural colour from an alkaline rock
Sodalite is commercially successful because its blue-and-white contrast reads immediately in cabochons, slabs and décor. The guide keeps the mineral distinct from lapis-lazuli and other mixed stones.
Collecting and care
Avoid acids and hard impact; clean with mild soapy water and a soft cloth. Protect polished surfaces from scratches and disclose whether a specimen is a rock aggregate or single mineral.
