Sodalite: Gemstones Information
Sodalite is Na8Al6Si6O24Cl2 and forms characteristic light to dark blue masses in the cubic system; the typically dodecahedral crystals are uncommon. The hardness is 5.5–6 and the SG 2.27–2.33. The RI is 1.483–1.487.The transparent colourless variety hackmanite from Dungannon Town ship, Ontario, Canada, shows bright orange under LWUV and bright pale pink under SW; after exposure to SW the colour may reach raspberry-reed but fades rapidly in sunlight. Further irradiation of the sample under SWUV repeats the cycle. Near-transparent dark blue crystals from Ohopoho, northern Namibia, have been faceted. Sodalite is found in the Ilimaussaq intrusion, southern Greenland and in the Khibiny and Lovozero massifs, Kola Peninsula, Russia. Sodalite is a major ingredient of the opaque ornamental rock lapis lazuli (q.v.).