Sodalite is a mineral with a hardness of 6 out of 10 on the Mohs scale of mineral hardness [?]. These Cubicly structured gems are made of sodium aluminum silicate, their full chemical compound being 3NaAlSiO4NaCl.
Sodalite is a sodium aluminum silicate chloride in the Sodalite group with an isometric crystal system. Its royal blue forms are the best known. As a mineral, it is a principal component of lapis lazuli.
It appears very rare as dodecahedrons, crystals with 12 faces, but usually it shows as compact masses, bright blue, white or gray with green tints. It is unsaturated and rarely appears with inclusions of pyrite, but is often mottled or veined (kind of like blue cheese with more royal blue in it) with nephelite, magnetite, mica, and cancrinite.
It is hard, light, fragile, with poor cleavage, and is translucent with vitreous luster. It is soluble in hydrochloric and nitric acid, leaving a silica gel. It fuses fairly easily to a colorless glass, coloring the flame yellow (sodium).
It is found with other feldspathoids (a group of rock-forming minerals similar to feldspars but deficient in silica) in silica-poor igneous rocks, in undersaturated plutonic igneous rocks (nepheline, syenites, and phonolites), and occurs with leucite, nepheline and cancricite. It is also found in volcanic blocks and in desilicified limestones that have reacted to hot fluids to produce new minerals.
Beautifully colored masses are found at Bancroft (Canada), Litchfield, Maine, and Magnet Cove, Arkansas (USA) and in smaller amounts in Brazil, Bolivia, Greenland, Romania, Portugal, Rhodesia, Burma, and Russia. Magnificent, clear crystals have been found in the calcium-carbonate-rich lavas of Vesuvius, in the Campi Fiegrei (Naples) and in the Monte Cimini (Viterbo), both in Italy. The most important deposit is in Bahia (Brazil).
Varieties of sodalite include:
Alomite – named after Charles Allom. This is a commercial term for blue sodalite, from Bancroft, Canada. It is an ornamental stone, also called 'princess blue' after Princess Patricia, a granddaughter of Queen Victoria, who favored this stone after first seeing it in Ontario.
Blue stone – a commercial term for sodalite. Mixed with creamy white, onyx marble, and used for inlay, it is also termed Canadian blue stone and princess blue.
Ditróite – a synonym for sodalite from Ditrau/Ditró, Transylvania (Romania).
Hackmanite – a transparent, pink, calcium and sulfur-rich variety of sodalite found at Mont St. Hilaire, Canada. It has tenebrescent qualities where its color can appear brightened when left in strong sunlight, but fade when kept in the dark or exposed to x-rays.
Sodalite can be confused with lapis lazuli, especially as pyrite, a feature that shows genuineness in lapis, can also be seen as occasional inclusions in sodalite. The safest method of differentiating is by comparing their specific gravity.
It can also be confused with azurite, dumortierite, haüynite, and lazulite.
Sodalite derives its name from sodium, the most dominant mineral it contains.
Sodalite is used in jewelry, as polished slabs and for carved ornaments. All shades of blue are found partly interspersed with white calcite. Wearers shound remember that its famous royal blue tends to lose its vividness when exposed to sunlight.
The dense aggregates are used for jewelry, but rarely faceted as gemstones. Mostly it is polished into cabochons, bead necklaces, pendants, fashion rings, and for other ornamental objects like sculptures, as its rich deep blue captures the elegance, for example, of eagles' wings.
Synthetic and imitations of sodalite are currently manufactured, but stones exhibiting its natural color are still more highly valued.