| Lazurite | |
|---|---|
| File:Lazuryt, Niemcy.jpg A lazurite specimen | |
| General | |
| Category | Mineral |
| Formula (repeating unit) | tectosilicate (Na,Ca)8(AlSiO4)6(SO4,S,Cl)2 |
| Crystal system | Isometric |
| Identification | |
| Color | Deep blue to greenish blue |
| Mohs scale hardness | 5-5.5 |
| Luster | translucent |
| Specific gravity | 2.4 |
| Refractive index | 1.5 |
| Fusibility | 3.5 |
| Solubility | Soluble in HCl |
Lazurite is a tectosilicate mineral with sulfate, sulfur and chloride with formula: (Na,Ca)8(AlSiO4)6(SO4,S,Cl)2. It is a feldspathoid and a member of the sodalite group. Lazurite crystallizes in the isometric system although well formed crystals are rare. It is usually massive and forms the bulk of the gemstone lapis lazuli.
Lazurite is a deep blue to greenish blue. It has a Mohs hardness of 5 to 5.5 and a specific gravity of 2.4. It is translucent with a refractive index of 1.50. It is fusible at 3.5 and soluble in HCl. It commonly contains or is associated with grains of pyrite.
Lazurite is a product of contact metamorphism of limestone and typically is associated with calcite, pyroxenes, and pyrite.
Other blue minerals such as the carbonate azurite and the phosphate lazulite may be confused with lazurite, but are easily distinguished with careful examination. Lazurite at one time was used as a synonym for azurite.
Lazurite has been mined for over 6,000 years in the lapis lazuli district of Badakhshan, Afghanistan. It has been used as a pigment in painting and cloth dyeing since at least the sixth or seventh century AD (Eastaugh 2004, p. 219). It is also mined at Lake Baikal in Siberia; Mount Vesuvius; Burma; Canada; and the United States (Eastaugh 2004, p. 219). The name is from the Persian lazward for blue.
