Article
Article
Lazurite
Article By:
Hurlbut, Cornelius S., Jr. Department of Geological Sciences, Harvard University, Cambridge, Massachusetts.
Last reviewed:November 2019
DOI:https://doi.org/10.1036/1097-8542.374200
The chief mineral constituent in the ornamental stone lapis lazuli. It crystallizes in the isometric system, but well-formed crystals, usually dodecahedral, are rare. Most commonly, it is granular or in compact masses. There is imperfect dodecahedral cleavage. The hardness is 5–5.5 on Mohs scale, and the specific gravity is 2.4–2.5. There is vitreous luster and the color is a deep azure, more rarely a greenish-blue (see illustration). Lazurite is a tectosilicate, the composition of which is expressed by the formula Na4Al3Si3O12S, but some S may be replaced by SO4 or Cl. Lazurite is soluble in HCl with the evolution of hydrogen sulfide.
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