Sodalite is a rich royal blue tectosilicate mineral widely used as an ornamental gemstone. Although massive sodalite samples are opaque, crystals are usually transparent to translucent. Sodalite is a member of the sodalite group with hauyne, nosean, lazurite and tugtupite.
First discovered by Europeans in 1811 in the Ilimaussaq intrusive complex in Greenland, sodalite did not become important as an ornamental stone until 1891 when vast deposits of fine material were discovered in Ontario, Canada.
7 See also
Sodalite is a cubic mineral which consists of an aluminosilicate cage network with Na+ cations in the interframework. This framework forms a cage structure, similar to zeolites. Each unit cell contains two cage structures. 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.
A sample of sodalite-carbonate pegmatite from Bolivia, with a polished rock surface.
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. The more uniformly blue material is used in jewellery, where it is fashioned into cabochons and beads. Lesser material is more often seen as facing or inlay in various applications.
Although somewhat similar to lazurite and lapis lazuli, sodalite rarely contains pyrite (a common inclusion in lapis) and its blue color is more like traditional royal blue rather than ultramarine. It is further distinguished from similar minerals by its white (rather than blue) streak. Sodalite’s six directions of poor cleavage may be seen as incipient cracks running through the stone.
Most sodalite will fluoresce orange under ultraviolet light, and hackmanite exhibits tenebrescence.
Parallel view (Stereogram guide parallel.png)
Cross-eye view (Stereogram guide cross-eyed.png)
Small specimen of Sodalite from Brazil.