Lazurite (Lapis Lazuli)

Category  :  Mineral
Hardness  :  5-5.5
Gravity  :  2.4
Reflection  :  1.50
Color  :  Deep blue to greenish blue
Chemical formula  :  (Na,Ca)8(AlSiO4)6(SO4,S,Cl)2
Crystal system  :  Isometric
Major varieties  :  Lapis Lazuli

Lapis Lazuli

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. It is also mined at Lake Baikal in Siberia; Mount Vesuvius; Burma; Canada; and the United States. The name is from the Persian lazward for blue.


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