Kutnohorite

Chemical formula: CaMn²⁺(CO₃)₂

Kutnohorite is a calcium manganese carbonate of the dolomite group, forming characteristic spherical aggregates with colors ranging from white and pink to brown.

## Characteristics Kutnohorite is a mineral of the dolomite group, being a calcium manganese carbonate. It forms a continuous isomorphic series with ankerite and dolomite. It rarely occurs in the form of well-developed, rhombohedral or prismatic crystals. Most commonly, it is found as massive, granular, fibrous, and radial or spherical aggregates. Its appearance can be unassuming, but well-formed, pink aggregates are valued by collectors. ## Physical Properties This mineral is characterized by a Mohs hardness of 3.5-4, making it relatively soft. It has a vitreous, sometimes dull luster. It is translucent. Its density is approximately 3.12 g/cm³, which is typical for carbonates. ## Colors and Varieties Kutnohorite ranges in color from white, through pale pink and pink, to light brown. The color depends on the manganese content – the more manganese, the more intense the pink color. Sometimes, the oxidation of manganese on the surface gives it a darker, brownish or blackish tarnish. No distinct commercial or gemological varieties are distinguished. ## History and Name The mineral's name comes from its discovery location – the historic mining town of Kutná Hora in the Czech Republic. It was first described in 1901 by Professor Antonín Bukovský. The type locality is Poličany, part of Kutná Hora. ## Uses Kutnohorite is primarily a mineral of interest to collectors and scientists. Due to its brittleness and relatively low hardness, it has no practical application in industry or jewelry.

Properties

Mohs hardness: 3.5-4
Luster: Vitreous
Streak: White
Density: 3.12
Cleavage: Perfect on <mi>{10_11}</mi>
Fracture: Sub-Conchoidal
Transparency: Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Kutnohorite is most easily recognized by its typical forms of occurrence – spherical or radial aggregates. Its characteristic pale pink to brown color is also distinctive. A key diagnostic feature, common to carbonates, is its vigorous reaction with hydrochloric acid (it effervesces). Hardness (3.5-4) and perfect cleavage are also helpful in identification. ## Distinguishing from Similar Minerals Kutnohorite is often confused with other carbonates of the dolomite group, especially dolomite and ankerite, with which it forms solid solutions. Differentiation without chemical analysis is often impossible. It can also be mistaken for rhodochrosite, which, however, usually has a more intense, cherry-red color. Calcite is slightly softer than kutnohorite (hardness 3). ## Crystal Forms Kutnohorite crystals are rare and usually take the form of small, curved rhombohedra. Much more often, it forms radial, spherulitic (spherical), fibrous, granular, or massive aggregates.

Geological environment

## Genesis Kutnohorite is a hydrothermal mineral, forming at low to medium temperatures. It forms in ore veins, often in association with other carbonates and sulfides. It is also found in metamorphic rocks that have undergone manganese metasomatism, and in some lacustrine sediments. ## Mineral Associations This mineral often co-occurs with rhodochrosite, aragonite, calcite, dolomite, ankerite, as well as sulfides such as pyrite, chalcopyrite, and sphalerite. Depending on the location, various manganese oxides may also accompany it. ## Localities The most important and historical occurrences of kutnohorite are in the Czech Republic, in the Kutná Hora region (type locality) and Chvaletice. Beautiful specimens come from the Wessels and N'Chwaning mines in Kuruman (South Africa). It is also known from Franklin and Sterling Hill in New Jersey (USA), Broken Hill in Australia, as well as from Italy (Piedmont area), Sweden (Långban), and Japan.

Rarity

Not very common

For collectors

## Quality Criteria The most valued by collectors are specimens with well-formed, spherical or radial aggregates of intense pink color. The absence of mechanical damage and aesthetic placement on the rock matrix are important. Contrast with associated minerals, e.g., white calcite, enhances the specimen's attractiveness. Large, well-formed crystals are exceptionally rare and sought after. ## Popular Localities Classic, though often less spectacular, specimens come from the type locality in the Czech Republic. The most desired on the collector's market are pink, spherical aggregates from manganese mines in the Kalahari region of South Africa (e.g., Wessels mine). Specimens from Franklin, USA, are also very popular.

Care and storage

## Cleaning Kutnohorite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. After wet cleaning, the specimen must be thoroughly dried. ## What to Avoid Kutnohorite is sensitive to acids – even weak ones, like vinegar, cause it to effervesce violently and decompose. Contact with household chemicals should be avoided. The mineral is brittle, so it must be protected from impacts and falls. Prolonged exposure to sunlight can cause some pink specimens to fade. ## Storage It is recommended to store kutnohorite in separate, padded boxes or display cases to prevent scratching by harder minerals. It should not be exposed to areas of high humidity or subject to rapid temperature changes.