Lazurite

 ( Sodalite Group ) 

Lazurite, old name Azure spar Krivovichev V. G. Mineralogical glossary. Scientific editor A. G. Bulakh. — St.Petersburg: St.Petersburg Univ. Publ. House. 2009. — 556 p. — ISBN 978-5-288-04863-0. (in Russian) is a tectosilicate mineral with sulfate, sulfur and chloride with formula . 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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Mineral Lazurite is a deep‐blue to greenish‐blue. The colour is due to the presence of anions. 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's fusibility scale, and soluble in HCl. It commonly contains or is associated with grains of pyrite.

Lazurite is a product of contact metamorphism of limestone and is typically associated with calcite, pyrite, diopside, humite, forsterite, hauyne and muscovite.

Other blue minerals, such as the carbonate mineral, azurite, and the phosphate mineral, lazulite, 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 District, Koksha Valley, Badakhshan 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 since at least the 6th or 7th century.

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

The most important mineral component of lapis lazuli is lazurite. (25% to 40%)

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Redefinition

Most lapis lazuli gets its blue color from Hauyne and almost none contain "true lazurite". This was changed in 2021, as lazurite was redefined so that it is enough for a quarter (instead of half) of the cages to contain sulfide.

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Structure

Lazurite and hauyne seem to have the same structure and both are sulfate-dominant minerals. Lazurite is a pigment (opalescent) and has a bright blue streak (especially as a component of the semiprecious stone lapis lazuli). Many hauynes have a white or pale blue streak and are translucent. The difference might be a consequence of the Redox potential (sulfate to sulfide ratio).

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See also

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External links

Categories: Sodalite Group, Sodium Minerals, Calcium Minerals, Aluminium Minerals, Pigments, Cubic Minerals, Minerals In Space Group 218

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