Sodalite

Sodalite forms in silica-poor alkaline rocks: nepheline syenites and other alkaline intrusions and pegmatites, carbonatites, metasomatised marbles and volcanic rocks. The type locality is the Ilímaussaq complex in Greenland. Canada produces large amounts of gem material, notably massive deep blue sodalite with reddish streaks from Bancroft, Ontario; very intense, sometimes nearly transparent blue material comes from Ohopoho, Namibia. Other sources include several US states, Afghanistan, Bolivia, Bahia in Brazil, Guinea, India, Myanmar, Norway, Russia and Scotland. Many sodalite beads and boxes are cut in Idar-Oberstein, Germany.

Sodalite can look like lapis lazuli and is sometimes offered as lapis, in error or to mislead; both can contain white calcite, but sodalite normally lacks lapis's pyrite inclusions. Its low refractive index (about 1.48) and specific gravity (about 2.3), and often an orangy red long-wave UV fluorescence, help separate it from other blue stones. The sulfur-rich variety hackmanite shows tenebrescence: it changes colour reversibly in sunlight and darkness. Heating can remove the colour and irradiation can restore it, and white sodalite may be dyed blue.

Sodalite is tough but scratches easily at hardness 5.5 to 6; quartz, topaz and even household dust can scratch it. Store it separately from other jewellery, use protective settings for rings, and clean it only with a soft brush, mild detergent and warm water.

Sodalite was described as a new mineral from Greenland by Thomas Thomson in 1811, and its name reflects its sodium content.

The Japanese retailer Pascle says sodalite is believed to strengthen its owner's will and determination when working toward a concrete goal. This is a retailer belief, not a tested property.