Lazurite | |
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General | |
Category | Tectosilicate |
Formula (repeating unit) | (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 in HCl |
References | [2][3][4][5][6] |
Lazurite, old name Azure spar[7]: 14 is a tectosilicate mineral with sulfate, sulfur and chloride with formula (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]. 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.