Sodalite
Sodalite (Cubic Sodalite Group) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Cubic (Isometric); usually occurs in massive, granular, or nodular forms rather than distinct crystals.
Mineral Group
Silicates (Tectosilicate); member of the Feldspathoid group
Chemical Formula
Na8(Al6Si6O24)Cl2
Formation Process
Igneous formation; specifically occurs in silica-poor igneous rocks such as nepheline syenites, phonolites, and associated pegmatites.
About This Crystal
Rich royal blue to violet-blue opaque body with characteristic white veining or mottled patches of calcite. This specimen shows a dull to vitreous luster and a smooth, polished surface with some internal fractures.
Physical Characteristics
Color: Blue with white streaks; Streak: White; Cleavage: Poor; Fracture: Uneven to conchoidal; Specific Gravity: 2.27–2.33; Fluorescence: Often strong orange-red under longwave UV.
Optical Properties
Isotropic (Singly refractive); Refractive Index: 1.483–1.487; Birefringence: None; Luster is vitreous to greasy.
Hardness & Durability
Origin Region
Notable sources include Bahia (Brazil), Bancroft (Ontario, Canada), Namibia, and the Kola Peninsula (Russia).
Hardness & Durability
Mohs Hardness: 5.5 to 6. Toughness is poor to fair; it is somewhat brittle and can be scratched by harder gemstones like quartz.
Care & Maintenance
Clean with warm soapy water only; avoid ultrasonic and steam cleaners. Sensitive to acids and sudden temperature changes. Store away from harder stones to prevent scratching.
Rarity & Value
Relatively common and affordable. Value is determined by the depth of the blue color and the aesthetic balance of the white calcite inclusions.
Special Characteristics
Tenebrescence (specifically in the Hackmanite variety); strong orange fluorescence under UV light; often mistaken for Lapis Lazuli but lacks the characteristic gold pyrite flecks.
Lore & History
First discovered in Greenland in 1811; became popular as an ornamental stone in 1891 after large deposits were found in Ontario. Historically used for carvings and jewelry; traditionally associated with logic, intuition, and the throat chakra.