Kutnohorite is a rare

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy u ...

carbonate mineral Carbonate minerals are those minerals containing the carbonate ion, . Carbonate divisions Anhydrous carbonates *Calcite group: trigonal **Calcite CaCO3 ** Gaspéite (Ni,Mg,Fe2+)CO3 **Magnesite MgCO3 ** Otavite CdCO3 **Rhodochrosite MnCO3 **Sid ...

with

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...

and

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in fr ...

that is a member of the dolomite group. It forms a series with dolomite, and with ankerite. The

end member An endmember (also end-member or end member) in mineralogy is a mineral that is at the extreme end of a mineral series in terms of purity of its chemical composition. Minerals often can be described as solid solutions with varying compositions of ...

formula is , but and commonly substitute for , with the manganese content varying from 38% to 84%, so the formula better represents the species. It was named by Professor Bukowsky in 1901 after the type locality of

Kutná Hora Kutná Hora (; medieval Czech: ''Hory Kutné''; german: Kuttenberg) is a town in the Central Bohemian Region of the Czech Republic. It has about 20,000 inhabitants. The centre of Kutná Hora, including the Sedlec Abbey and its ossuary, was design ...

, Bohemia, in the Czech Republic.Frondel, Clifford and Bauer, L H (1955), Kutnahorite, a manganese dolomite, . American Mineralogist 40: 748 It was originally spelt "kutnahorite" but "kutnohorite" is the current IMA-approved spelling.

Dolomite group

* dolomite, * Ankerite, *Kutnohorite, *

Minrecordite Minrecordite, CaZn(CO3)2 , is a very rare mineral belonging to the dolomite group, the member with Ca and Zn. It was discovered, associated with dioptase, in a specimen from the Tsumeb mine (Namibia), which is consequently its type locality. Its ...

Unit cell

There are three formula units per

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...

(Z = 3) and the lengths of the sides are a close to 4.9 Å and c between 16 Å and 17 Å, although different sources give slightly different values, as follows: :a = 4.915 Å, c = 16.639 Å :a = 4.8518(3) Å, c = 16.217(2) Å :a = 4.85 Å, c = 16.34 Å

Structure

The crystal class is

trigonal In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal ...

space group In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unch ...

R, the same as for the other members of the dolomite group. There are layers of groups perpendicular to the long

crystal axis In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns th ...

c, and between these layers there are layers of the

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

and . If there were perfect ordering amongst the cations they would separate into different layers, giving rise to the ordered sequence: along the c axis; not all specimens, however, display such ordering.Peacor, D R, Essene, E J and Gaines, A M (1987) Petrologic and crystal-chemical implications of cation order-disorder in kutnahorite. American Mineralogist 72:319

Optical properties

Kutnohorite may be white, pale pink or light brown. The pink shades are due to increased

and the brown colours are due to increased

content. The mineral is translucent with a white to pale pink streak and vitreous to dull luster. It is uniaxial (-) with

refractive indices In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

N_o = 1.710 to 1.727 and N_e = 1.519 to 1.535, similar to dolomite. The ordinary refractive index, N_o, is high, comparable with

spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals. Properties S ...

(1.719).

Physical properties

Kutnohorite occurs as aggregates of bundled blades of white through rose pink to light brown crystals. Also as simple rhombs with curved faces,

polycrystal A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains. Bacillite is a type of crystallite. It is rodlike with parallel longulites. Stru ...

line spherules and in massive and granular habits. It has perfect rhombohedral cleavage, typical of

carbonates A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

. It is brittle with a subconchoidal

fracture Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displ ...

and it is quite soft, with

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

3.5 to 4, between

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

and

fluorite Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. The Mohs scale ...

Specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

is 3.12, denser than both dolomite and calcite. It is soluble in

acids In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...

, as are all carbonates.

Occurrence

Kutnohorite occurs typically in manganiferous sediments, associated with

rhodochrosite Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its (rare) pure form, it is typically a rose-red color, but impure specimens can be shades of pink to pale brown. It streaks white, and its Mohs hardness varies bet ...

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pr ...

and

. Notable occurrences include

Tuscany it, Toscano (man) it, Toscana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Citizenship , demographics1_footnotes = , demographics1_title1 = Italian , demogra ...

, Italy and

, Czech Republic. It probably occurs at the

Trepča Mines The Trepča Mines ( al, Miniera e Trepçës, sr, Рудник Трепча / ''Rudnik Trepča'') is a large industrial complex in Kosovo, located northeast of Mitrovica. The mine is located on the southern slopes of the Kopaonik mountain, bet ...

, Stari Trg, Kosovo, in the Balkans.The Mineralogical Record (2007) 38-4:284 At the Eldorado Mine,

Ouray County, Colorado Ouray County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 4,874. The county seat is Ouray. Because of its rugged mountain topography, Ouray County is also known as the Switzerland of America. H ...

, US, it occurs as tiny white crystals partially encrusting

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical fo ...

and dolomite.Rocks & Minerals (2009) 84-5:423 At the Ryujima Mine,

Nagano Prefecture is a landlocked prefecture of Japan located in the Chūbu region of Honshū. Nagano Prefecture has a population of 2,052,493 () and has a geographic area of . Nagano Prefecture borders Niigata Prefecture to the north, Gunma Prefecture to the nort ...

in Japan, magnesian kutnohorite occurs with

and

.Akio Tsusue (1967) Magnesian Kutnahorite from Ryujima Mine, Japan. American Mineralogist 52:1751 The type locality is Poličany,

, Central Bohemia Region, Bohemia, Czech Republic, and type material is conserved at

Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher le ...

, Cambridge, Massachusetts, US.

References

External links

*JMol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=01069 {{Manganese minerals Carbonate minerals Manganese(II) minerals Dolomite group Trigonal minerals Minerals in space group 148