Kutnohorite

Kutnohorite occurs as aggregates of bundled blades of white through rose pink to light brown crystals. Also as simple rhombs with curved faces, polycrystalline spherules and in massive and granular habits. It has perfect rhombohedral cleavage, typical of carbonates. It is brittle with a subconchoidal fracture and it is quite soft, with hardness 3.5 to 4, between calcite and fluorite. Specific gravity is 3.12, denser than both dolomite and calcite. It is soluble in acids, as are all carbonates.

Kutnohorite occurs typically in manganiferous sediments, associated with rhodochrosite, aragonite and calcite. Notable occurrences include Tuscany, Italy and Kutná Hora, Czech Republic. It probably occurs at the Trepča Mines, Stari Trg, Kosovo, in the Balkans. At the Eldorado Mine, Ouray County, Colorado, US, it occurs as tiny white crystals partially encrusting quartz and dolomite. At the Ryujima Mine, Nagano Prefecture in Japan, magnesian kutnohorite occurs with quartz and rhodochrosite. The type locality is Poličany, Kutná Hora, Central Bohemia Region, Bohemia, Czech Republic, and type material is conserved at Harvard University, Cambridge, Massachusetts, US.

The crystal class is trigonal 3, space group R3, the same as for the other members of the dolomite group. There are layers of (CO3)(−2 groups perpendicular to the long crystal axis c, and between these layers there are layers of the cations Ca and Mn. If there were perfect ordering amongst the cations they would separate into different layers, giving rise to the ordered sequence: Ca−(CO3)−Mn−(CO3)−Ca−(CO3)−Mn−(CO3)− along the c axis; not all specimens, however, display such ordering.