Sodalite

Hardness: 5.5-6.0 Mohs; Color: Royal blue, grey, or white; Luster: Vitreous to greasy; Crystal Structure: Isometric (cubic); Cleavage: Poor; Specific Gravity: 2.27-2.33

Forms in silica-poor igneous rocks such as nepheline syenites and phonolites. It can also form during hydrothermal metasomatism of lime-rich rocks.

Used primarily as decorative stone, in jewelry (beads, cabochons), and as a collecting specimen. Historically used as a pigment.

Sodalite is often mistaken for Lapis Lazuli, but unlike Lapis, it rarely contains golden pyrite inclusions and has a lower density. It is famous for its occurrences in Bancroft, Ontario, and is sometimes called 'Princess Blue' because it was selected as a decorative stone for Marlborough House in London.

Identify by its deep blue color often mottled with white calcite veins. In the field, look for it in alkaline igneous complexes. Unlike Azurite, it will not react with dilute acid.