Kutnohorite

Kutnohorite
Kutnohorite, Wessels Mine, Kalahari manganese fields, Northern Cape Province, South Africa. Size 4.4 x 4.2 x 1.9 cm
General
Category	Carbonate mineral
Formula (repeating unit)	CaMn2+(CO3)2
IMA symbol	Kut[1]
Strunz classification	5.AB.10
Dana classification	14.2.1.3
Crystal system	Trigonal
Crystal class	Rhombohedral (3) H-M symbol: (3)
Space group	R3
Unit cell	330.60 ų
Identification
Formula mass	215.0 g/mol (end member)
Color	White, pale pink or light brown
Crystal habit	Aggregates of bundled bladed crystals
Cleavage	Perfect on {1011}
Fracture	Subconchoidal
Tenacity	Brittle
Mohs scale hardness	3.5–4
Luster	Vitreous to dull
Streak	White to pale pink
Diaphaneity	Translucent
Specific gravity	3.12
Density	3.10–3.12
Optical properties	Uniaxial (−)
Refractive index	no = 1.710–1.727, ne = 1.519–1.535
Birefringence	0.191–0.192
Solubility	Soluble in acids
References	[2][3][4][5]

Kutnohorite is a rare calcium manganese carbonate mineral with magnesium and iron that is a member of the dolomite group. It forms a series with dolomite, and with ankerite. The end member formula is CaMn²⁺(CO₃)₂,^[6] but Mg²⁺ and Fe²⁺ commonly substitute for Mn²⁺, with the manganese content varying from 38% to 84%,^[2] so the formula Ca(Mn²⁺,Mg,Fe²⁺)(CO₃)₂ better represents the species. It was named by Professor Bukowsky in 1901 after the type locality of Kutná Hora, Bohemia, in the Czech Republic.^[7] It was originally spelt "kutnahorite" but "kutnohorite" is the current IMA-approved spelling.