Sodalite

Hardness: 5.5-6 on Mohs scale. Color: Typically intense royal blue, but can also be grey, green, pink, or yellow. Often with white streaks or veins of calcite. Luster: Vitreous to greasy. Crystal structure: Isometric (cubical), but crystals are rare; usually found in massive, granular, or nodular forms. Cleavage: Poor in six directions. Specific Gravity: 2.13-2.29.

Sodalite forms in igneous rocks that are rich in sodium and relatively poor in silica, such as nepheline syenites. It crystallizes from alkali-rich, silica-undersaturated magma. It can also be found in metamorphic rocks (e.g., marbles). Geological age varies depending on the specific igneous or metamorphic event.

Primarily used as an ornamental stone and in jewelry (beads, cabochons, carvings) due to its attractive blue color. It can also be carved into small sculptures or used as an inlay material. It is not typically used in heavy industry or construction.

Sodalite is a member of the sodalite group of minerals. It is often confused with Lapis Lazuli, but sodalite typically lacks the golden pyrite flecks common in lapis and often has distinct white calcite streaking. Some sodalite exhibits tenebrescence (also known as reversible photochromism), meaning it can change color when exposed to light (e.g., Hackmanite, a variety of sodalite, which can turn pink or violet when exposed to UV light and then fade over time).

In the field, sodalite can be identified by its distinctive blue color, relatively low hardness (easily scratched with a steel file), and presence of white veining. A definitive test is its lack of reaction to an acid drop (unlike calcite which would effervesce). Common locations include Bancroft, Ontario, Canada; Litchfield, Maine, USA; Russia (Kola Peninsula); Brazil; and Namibia. For collectors, raw specimens with good color and distinct mineral associations are sought after, as are well-polished jewelry pieces.