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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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