Lazurite

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.

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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 was first described in 1890 from the lapis lazuli district of Badakhshan, Afghanistan. The name is from the Persian lazward for blue.

References

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, ISBN 0-471-80580-7
• Mindat with location data
• Mineral galleries
• Webmineral data