sodalita

Sodalite is a tectosilicate mineral composed of sodium aluminium silicate with the chemical formula Na8(Al6Si6O24)Cl2. It is a member of the sodalite group, which also includes hackmanite, nosean, and tugtupite. Sodalite is found in igneous rocks, particularly in alkali-rich, silica-poor rocks like nepheline syenites and sodalite-bearing syenites. It can also occur in metamorphic rocks and as a byproduct of volcanic activity.

Sodalite is typically found in massive form, though well-formed crystals are known. Its color is most commonly a rich royal blue, but it can also be white, gray, green, or yellow. The blue color is usually due to the presence of sulfur impurities. Sodalite is known for its fluorescence under ultraviolet light, often emitting a yellow or orange glow.

The mineral was first discovered in 1811 in the Ilimaussaq intrusion in Greenland. It gained prominence in 1891 when large deposits were found in Bancroft, Ontario, Canada, leading to its widespread use as a gemstone and ornamental material. Sodalite is relatively soft, with a Mohs hardness of 5.5 to 6, making it susceptible to scratching. It is often cut into cabochons, beads, and used for carvings. Sodalite is also a valuable mineral for scientific study, particularly in understanding the formation and evolution of alkaline igneous rocks.