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| Formula | MnCO3 |
| | Optic class & sign | Uniaxial negative |
| | Relief | Moderate to high |
| | Refractive indices | no = 1.816
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ne = 1.597
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| n and Δn data for endmember composition; n increases with increasing Fe and Zn, decreases with increasing Ca or Mg. |
| | Birefringence (max.) | 0.219 |
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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 to pale pink, weakly pleochroic (O>E) if coloured. |
| | Zoning | Colour zoning may be present |
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| Form | Habit | Granular, botroidal |
| | | Surface | Anhedral, rarely euhedral |
| | Cleavage | 3 sets, rhombohedral {1011} |
| | Twinning | Lamellar and contact on {1021}, rare |
| | 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 | Mn-oxides and -hydroxides |
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| Occurence | Ign | Carbonatites, rare in pegmatite |
| | | Met | Mn-rich metamorphic rocks |
| | | Sed | Authigenic and secondary in Mn-rich sediments |
| | | Hyd | Low- to moderate-temperature hydrothermal veins |
| | | 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). Rhodochrosite is pink-pleochroic (if coloured); alteration; mineral association.
Rhodochrosite, smithsonite 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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