Lazurite

Lazurite is a tectosilicate mineral with sulfate with formula (Na,Ca)8 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. The colour is due to the presence of S− 3 It has a Mohs hardness of 5.0 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 on Wolfgang Franz von Kobell scale, and soluble in HCl. It commonly contains or is associated with grains of pyrite.

Lazurite is a product of contact metamorphism of limestone , pyrite, diopside , hauyne

Other blue minerals, such as the carbonate and the phosphate , may be confused with lazurite, but are easily distinguished with careful examination. At one time, lazurite was a synonym for azurite

Lazurite was first described in 1890 for an occurrence in the Sar-e-Sang Province, Afghanistan It has been mined for more than 6,000 years in the lapis lazuli district of Badakhshan. It has been used as a pigment in painting and cloth dyeing It is also mined at Lake Baikal ; Burma; Canada; and the United States. The name is from the Persian