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| Formula | ZnCO3 |
| | Optic class & sign | Uniaxial negative |
| | Relief | Moderate to high |
| | Refractive indices | no = 1.850
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ne = 1.625
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| n and Δn data for endmember composition; n decreases with increasing Mg, Mn and Ca |
| | Birefringence (max.) | 0.225 |
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| | Sign of elongation | Hardly applicable due to very high Δn |
| | Interference figure | Well-defined isogyre cross, isochromes over multiple colour orders |
| | Colour / pleochroism | Colourless |
| | Zoning | |
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| Form | Habit | Granular, botroidal |
| | | Surface | Commonly anhedral; faces are typically curved where present |
| | Cleavage | 3 sets, rhombohedral {1011} |
| | Twinning | Not observed |
| | Extinction | Symmetrical to cleavage traces in sections subparallel to c. Mottled extinction due to abundant miniscule breakouts at cleavage intersections. |
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| Reaction textures | |
| | Alteration / decomposition | Hemimorphite, limonite |
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| Occurence | Ign | |
| | | Met | |
| | | Sed | |
| | | Hyd | Secondary in oxidised zones of ore deposits containing Zn |
| | | Other | |
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| Distinctive properties | High-order white interference colours, rhombohedral cleavage, and relief change between nO and nE (as for all other rhombohedral carbonates). Mineral association. Lack of lamellar twins.
Smithsonite, rhodochrosite and siderite are distinguished from the other rhombohedral carbonates by their distinctly higher n (both nO and nE; no negative relief in any position). |
| | Additional comments | n-Δn chart: Cal - calcite, Dol - dolomite, Kut - kutnahorite, Mgs - magnesite, Rds - rhodochrosite, Sid - siderite, Smt - smithsonite |
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