Sodalite

Sodalite is a rich, royal blue mineral widely used as an ornamental gemstone. While it can look similar to lapis lazuli, it is typically a more saturated blue and rarely contains the golden pyrite flecks common in lapis. Instead, it is often crisscrossed with white veins of calcite. Its name refers to its high sodium content.

Formation & Geology

Sodalite is a member of the feldspathoid group and forms in silica-poor igneous rocks (syenites and trachytes) and their associated pegmatites. It is rarely found in crystals and usually occurs in massive, granular forms. A unique variety called 'Hackmanite' shows 'tenebrescence'—it changes color when exposed to sunlight and fades back in the dark.

Physical Characteristics

Sodalite has a hardness of 5.5 to 6, making it suitable for carvings and beads but somewhat soft for rings. It has a vitreous to greasy luster and is typically translucent to opaque. It belongs to the isometric (cubic) crystal system, though distinct crystals are extremely rare. The most defining feature is its deep blue color, which is caused by the presence of chlorine in its structure.

Historical Significance & Uses

Sodalite was first discovered in Greenland in 1811 but didn't become popular until 1891, when vast deposits were found in Ontario, Canada. It became known as 'Princess Blue' after Princess Margaret of England visited Canada and chose sodalite for the interior decoration of Marlborough House. Today, it is used for beads, cabochons, carvings, and even large architectural slabs for countertops and flooring.