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| Formula | (Zn,Fe)S |
| | Optic class & sign | Isotropic |
| | Relief | Extreme |
| | Refractive Index | 2.37 -2.50
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| n increases with increasing Fe content |
| | Birefringence | Δn increases with increasing amount of wurtzite in the structure |
| | Colour | Colourless, pale yellow, pale brown; opaque if Fe-rich |
| | Zoning | |
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| Form | Habit | Granular, tetrahedral or dodecahedral habit; may have curved faces; less commonly fibrous |
| | | Surface | Euhedral to anhedral |
| | Cleavage | {110} six sets |
| | Twinning | {111} and {211} contact twins, simple or multiple, lamellar intergrowths; twins are only observed if grains are birefringent or re-entrant crystal faces are visible. |
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| Reaction textures | |
| | Alteration / decomposition | Smithsonite, hemimorphite, oxides, hydroxides, sulfates, carbonates |
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| Occurence | Ign | Rare in granite or pegmatite, ultramafic rocks |
| | | Met | Metamorphosed Zn-bearing rocks, contact-metasomatic deposits |
| | | Sed | Syngenetic in coal and concretionary masses, in limestone |
| | | Hyd | Hydrothermal sulfide deposits, low- to high-temperature |
| | | Other | Minor phase in meteorites |
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| Distinctive properties | Extreme relief, isotropy, cleavage |
| | Additional comments | Wurtzite (α-ZnS) is uniaxial-positive, with nO = 2.356, nE = 2.378, Δn = 0.022 |
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