Kutnohorite
Kutnohorite is CaMn(CO3)2, the manganese dolomite-group carbonate: pink to white, hardness 3.5 to 4, density 3.12 against rhodochrosite's 3.70. Named 1903.
Kutnohorite is CaMn(CO3)2, the manganese member of the dolomite group, named for Kutná Hora in the Czech Republic and first described in 1903. It is white to bright pink, hardness 3.5 to 4, measured density 3.12, with rhombohedral cleavage. Its density sits between magnesite's 3.00 and rhodochrosite's 3.70, which is the practical way to separate it.
In short
- The IMA name is kutnohorite; the older spelling kutnahorite is the one on many labels, and the Handbook of Mineralogy cites Frondel and Bauer's 1955 paper, a manganese dolomite, under it. Both name the same species, which the September 2026 IMA-CNMNC Master List lists as grandfathered, 1903, Czech Republic.
- It is dolomite with manganese in place of magnesium. Dolomite is CaMg(CO3)2, ankerite CaFe2+(CO3)2 and kutnohorite CaMn(CO3)2 on the IMA list, and the dolomite sheet records series with both ankerite and kutnohorite. The Handbook's group note: ordered Ca:Mn ≈ 1:1, commonly with substitution by Mg and Fe2+.
- Worked from standard atomic weights, ideal kutnohorite is 32.99% MnO, 26.08% CaO and 40.93% CO2, exactly the sheet's calculated column. That is 25.55% manganese by mass, against 47.79% in rhodochrosite.
- Density is the working test against pink rhodochrosite: 3.12 against 3.70, an 18.6% gap. Of the six calcite- and dolomite-group sheets in this site's 176-sheet reference set, none has a measured density between magnesite's 3.00 and rhodochrosite's 3.70.
- Three kutnohorite localities are also on the rhodochrosite sheet: the N’Chwaning mine near Kuruman, South Africa, which the Handbook singles out for fine kutnohorite; the Sunnyside mine near Silverton, Colorado; and Mont Saint-Hilaire, Quebec.
| Species | Formula | Group | Hardness | Density (meas.) | ω | Colour, per the sheet |
|---|---|---|---|---|---|---|
| Kutnohorite | CaMn(CO3)2 | Dolomite | 3.5 to 4 | 3.12 | 1.710 to 1.727 | White, pale pink to bright pink |
| Dolomite | CaMg(CO3)2 | Dolomite | 3.5 to 4 | 2.86 | 1.679 | Colourless, white, yellow, brown, pale pink |
| Calcite | CaCO3 | Calcite | 3 | 2.7102 | 1.658 | Colourless or white, also grey, yellow, green, other colours from inclusions |
| Magnesite | MgCO3 | Calcite | 3.5 to 4.5 | 3.00 | 1.700 | Colourless, white, pale yellow, pale brown, faintly pink, lilac-rose |
| Rhodochrosite | MnCO3 | Calcite | 3.5 to 4 | 3.70 | 1.810 | Pink, rose-red, cherry-red, yellow and others |
| Siderite | FeCO3 | Calcite | 3.75 to 4.25 | 3.96 | 1.875 | Yellowish brown, brown; white, ash-grey, yellowish grey, pale green |
| Smithsonite | ZnCO3 | Calcite | 4 to 4.5 | 4.43 | 1.842 to 1.850 | White, greys, browns; more rarely pink, green, blue and others |
What kind of mineral is kutnohorite?
A calcium manganese carbonate with the dolomite structure. The IMA formula is CaMn(CO3)2; the Handbook writes Ca(Mn2+,Mg,Fe2+)(CO3)2 to show that magnesium and ferrous iron commonly share the manganese site. It is hexagonal, occurs as polycrystalline spherules, to 2 cm, aggregates, and cleavages, and is white or pale to bright pink.
The sheet gives its setting as typically in deposits associated with manganiferous sediments, with rhodochrosite, aragonite and calcite. Its distribution list opens with a qualifier worth noticing: analyzed material, shown to have the dolomite structure type. A pink carbonate from a manganese deposit is not kutnohorite until someone has shown that.
Several physical properties are printed in square brackets on the sheet, and the cleavage line says why: by analogy to dolomite group. The perfect rhombohedral cleavage, subconchoidal fracture, brittleness and the hardness of 3.5 to 4 are therefore the group's, not measurements on kutnohorite itself. The density, 3.12 measured and 3.15 calculated, and the optics are its own.
Kutnohorite, dolomite and ankerite: one structure, three cations
On the September 2026 IMA list the three are written identically except for one cation: dolomite CaMg(CO3)2 (grandfathered, 1792, Italy), ankerite CaFe2+(CO3)2 (1825, Austria) and kutnohorite CaMn(CO3)2 (1903, Czech Republic). The kutnohorite sheet records two series, with dolomite, and with ankerite, and the dolomite sheet returns the favour. Across the 176 sheets in this site's reference set, dolomite's is the only one filed under Dolomite group and the only one that names kutnohorite; the method was pdftotext -layout and a case-insensitive regular expression covering both spellings of the name.
A worked calculation shows how far real kutnohorite strays from the ideal. Take the sheet's two analyses, divide each oxide by its formula mass (CaO 56.077, MnO 70.937, MgO 40.304, FeO 71.844, from standard atomic weights) and scale the four cations to a total of 2, as in CaMn(CO3)2:
- Kutná Hora, the first described occurrence: Ca 0.91, Mn 0.70, Mg 0.27, Fe 0.12.
- Franklin, New Jersey: Ca 1.03, Mn 0.84, Mg 0.12, Fe 0.01.
In both, manganese is the largest of the three non-calcium cations, which is what makes the material kutnohorite rather than dolomite or ankerite. But the type specimen carries more than a quarter of an atom of magnesium, and its calcium falls below 1, so some of the other cations must sit on the calcium site. The ideal formula, run the same way, gives 32.99% MnO, 26.08% CaO and 40.93% CO2 (formula mass 215.032), which is the sheet's third column to the hundredth.
How to tell kutnohorite from rhodochrosite
Both are pink, both cleave rhombohedrally, both are hardness 3.5 to 4, and the kutnohorite sheet lists rhodochrosite as its first associate. Hardness and cleavage will not separate them; density and refractive index will.
Density. Kutnohorite measures 3.12 and rhodochrosite 3.70, a gap of 18.6%. Of the six calcite-group and dolomite-group sheets in the 176-sheet set (calcite, magnesite, rhodochrosite, siderite, smithsonite, dolomite), none falls between magnesite's 3.00 and rhodochrosite's 3.70, so a clean pink cleavage fragment that measures near 3.1 is not behaving as rhodochrosite. The method is on how to measure specific gravity at home.
The caveat is in the rhodochrosite sheet itself: it forms a series with calcite, so calcian rhodochrosite and manganoan calcite are real and fall between the end members. A reading between 3.12 and 3.70 on its own names nothing. Neither does colour: kutnohorite's white, pale pink to bright pink sits inside rhodochrosite's range. The refractive index ω, 1.710 to 1.727 against rhodochrosite's 1.810, is the cleaner single figure, and an analysis or X-ray pattern is what fixes the name. A pink carbonate with a pink silicate beside it is a separate question, answered on is rhodochrosite the same as rhodonite.
Where kutnohorite is found
The Handbook's localities for analysed material: Kutná Hora and Chvaletice, Czech Republic; Långban, Värmland, Sweden; near Levane, Tuscany; Franklin and Sterling Hill, Ogdensburg, New Jersey; the Sunnyside and Silver King mines, Silverton district, Colorado; the Longvale quarry, Laytonville, California; Bald Knob, North Carolina; Mont Saint-Hilaire, Quebec; the Providencia district, Zacatecas, Mexico; fine examples from the N’Chwaning mine, near Kuruman, South Africa; the Hoei tin mine, the Chichibu mine and the Ryujima mine in Japan; and Broken Hill, New South Wales.
No British locality is on the sheet. The name comes from the first described occurrence at Kutná Hora, and the sheet notes that the original label was translated as kutnohorite, which is the form the IMA uses. The type material is at Harvard University.
The rest of this reference section is indexed at the species index. There is no catalogue here and nothing here is offered for sale; the wanted list is the only commercial route.