Lazurite
Lazurite 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.
| Lazurite | |
|---|---|
Lazurite, Ladjuar Medam (Lajur Madan; Lapis-lazuli Mine), Sar-e-Sang District, Koksha Valley (Kokscha; Kokcha), Badakhshan (Badakshan; Badahsan) Province, Afghanistan | |
| General | |
| Category | Tectosilicate |
| Formula (repeating unit) | (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)] |
| IMA symbol | Lzr |
| 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 | |
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