Sodalite
Sodalite is a member of the Sodalite mineral group that also includes Hackmanite, Tugtupite, and Lazurite. The Sodalite mineral group is named after its most common member. Sodalite is also one of the members of the Feldspathoid group of minerals that includes Cancrinite, Haüyne, Lazurite, Leucite, Nepheline, and Sodalite. Minerals with chemistries that are close to those of the alkali Feldspars, but are poor in silica (SiO2) content, are called Feldspathoids. Sodalite is mostly known for vivid blue, opaque material that is seldom transparent and clean enough for faceting. Faceted gems are very rare and usually very small.
Although Sodalite is found in several localities around the world, few of these produce transparent crystals for faceting. A recent find in Afghanistan has produced some beautiful, colorless, very clean gems. Other locations such as Bancroft, Ontario, Canada are the source of small, semi-transparent, vivid blue gems.
| Category: | Tectosilicates without zeolitic H2O |
| Formula: | Na8(Al6Si6O24)Cl2 |
| Crystallography: | Isometric – Hextetrahedral |
| Crystal Habit: | Crystals rare, typically dodecahedra, to 10 cm; as embedded grains or massive. |
| Twinning: | Common, forming pseudohexagonal prisms. |
| Cleavage: | [110] Poor |
| Fracture: | Conchoidal to Uneven, Irregular |
| Tenacity: | Brittle |
| Hardness (Mohs): | 5.5 – 6.0 |
| Density: | 2.27 – 2.33 (g/cm3) |
| Luminescence: | Bright red-orange under SW and LW UV. cathodoluminescent. Yellowish phosphorescence may be photochromic in magentas. |
| Radioactivity: | Not Radioactive |
| Color: | Colorless, White, Yellowish, Greenish, Gray, light to dark Blue, Azure Blue, Pink |
| Transparency: | Transparent to Translucent |
| Luster: | Vitreous, Greasy |
| Refractive Index: | 1.483 – 1.487 Isotropic |
| Birefringence: | 0.00 (Isotropic) |
| Dispersion: | 0.018 |
| Pleochroism: | None |
