| Lazurite | |
|---|---|
 Lazurite, Ladjuar Medam (Lajur Madan; Lapis-lazuli Mine), Sar-e-Sang District, Koksha Valley (Kokscha; Kokcha), Badakhshan (Badakshan; Badahsan) Province, Afghanistan | |
| General | |
| Category | Tectosilicateminerals,feldspathoidgroup,sodalite group |
| Formula | (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)] |
| IMA symbol | Lzr[1] |
| Strunz classification | 9.FB.10 |
| Crystal system | Isometric |
| Crystal class | Hextetrahedral (43m) H-M symbol: (4 3m) |
| Space group | P43n |
| Unit cell | a = 9.09 Å; Z = 2 |
| Identification | |
| Color | Deep blue, azure, violet-blue, greenish blue |
| Crystal habit | Crystals occur as dodecahedra, or rarely cubes; granular, disseminated, or massive |
| Cleavage | Imperfect on {110} |
| Fracture | Uneven |
| Tenacity | Brittle |
| Mohs scale hardness | 5–5.5 |
| Luster | Vitreous |
| Diaphaneity | Translucent to opaque |
| Specific gravity | 2.38–2.45 |
| Optical properties | Isotropic; anomalously anisotropic |
| Refractive index | 1.502–1.522 |
| Fusibility | 3.5 |
| Solubility | Soluble inHCl |
| References | [2][3][4][5][6] |
Lazurite, old nameAzure spar[7]: 14 is atectosilicate mineral withsulfate,sulfur andchloride with formula(Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]. It is afeldspathoid and a member of thesodalite group. Lazurite crystallizes in theisometric system although well‐formed crystals are rare. It is usually massive and forms the bulk of the gemstonelapis lazuli.
Lazurite is a deep‐blue to greenish‐blue. The colour is due to the presence ofS−
3 anions.[8] It has aMohs hardness of 5.0 to 5.5 and aspecific gravity of 2.4. It is translucent with arefractive index of 1.50. It is fusible at 3.5 onWolfgang Franz von Kobell'sfusibility scale, and soluble inHCl. It commonly contains or is associated with grains ofpyrite.
Lazurite is a product ofcontact metamorphism oflimestone and is typically associated withcalcite, pyrite,diopside,humite,forsterite,hauyne andmuscovite.[2]
Other blue minerals, such as thecarbonate mineral,azurite, and thephosphate mineral,lazulite, may be confused with lazurite, but are easily distinguished with careful examination. At one time, lazurite was a synonym forazurite.[5]
Lazurite was first described in 1890 for an occurrence in theSar-e-Sang District,Koksha Valley,Badakhshan Province,Afghanistan.[3] It has been mined for more than 6,000 years in thelapis lazuli district of Badakhshan. It has been used as a pigment in painting and clothdyeing since at least the 6th or 7th century.[9] It is also mined atLake Baikal in Siberia;Mount Vesuvius;Burma;Canada; and theUnited States.[9] The name is from thePersianlajvard for blue.[10]
The most important mineral component of lapis lazuli islazurite[11] (25% to 40%)[citation needed]
Most lapis lazuli gets its blue color from Hauyne and almost none contain "true lazurite".[11] 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.[12]
Lazurite andhauyne seem to have the same structure and both are sulfate-dominant minerals.[13] Lazurite is apigment (opalescent) and has a bright blue streak (especially as a component of the semiprecious stonelapis lazuli). Many hauynes have a white or pale blue streak and are translucent. The difference might be a consequence of theredox state (sulfate to sulfide ratio).[8][14]
Media related toLazurite at Wikimedia CommonsGemmological classifications by E. Ya. Kievlenko (1980), updated | |||||||||
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