Tetrahedrite-(Mn)

Chemical formula: Cu₁+₆(Cu₁+₄Mn₂+₂)Sb₃+₄S₂-₁₃

A rare sulfosalt from the tetrahedrite group, in which manganese is the dominant divalent metal, forming black, metallic crystals.

## Characteristics Tetrahedrite-(Mn) is a mineral belonging to the tetrahedrite group, where manganese (Mn) replaces other divalent metals such as iron, zinc, or mercury. Visually, it is indistinguishable from other minerals in this group, especially tetrahedrite-(Fe) and tetrahedrite-(Zn). It forms crystals with a characteristic tetrahedral shape, from which the group's name is derived. It usually occurs in granular or massive aggregates. The surface of the crystals is often covered with triangular growth patterns. ## Physical Properties This mineral is characterized by a metallic luster and is opaque. Its Mohs hardness ranges from 3.5 to 4, which means it is relatively soft. It is a brittle mineral, and its fracture is uneven to conchoidal. ## Colors and Varieties Tetrahedrite-(Mn) is steel-gray to black in color. Its streak is black, sometimes with a brownish tint. There are no distinct color or commercial varieties; identification of individual members of the tetrahedrite group requires advanced chemical analysis. ## History and Name The name "tetrahedrite" comes from the Greek word "tetraedron," meaning "tetrahedron," which refers to the typical form of its crystals. The suffix "-(Mn)" was added according to the naming rules of the International Mineralogical Association (IMA) in 2019 (IMA 19-B) to indicate that manganese is the dominant divalent metal in this particular mineral. This change was part of a larger reclassification of the entire tetrahedrite group.

Properties

Mohs hardness: 3.5-4
Luster: Metallic
Streak: Black
Density: 4.9-5.1
Cleavage: None
Fracture: Uneven to sub-conchoidal
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Visual identification of tetrahedrite-(Mn) is impossible without chemical analysis. In the field or in a collection, it can be identified as a member of the tetrahedrite group based on its regular crystallographic system, crystal form (tetrahedra), steel-gray to black color, metallic luster, and black streak. It is relatively soft and brittle. ## Distinguishing from Similar Minerals It can be confused with other members of the tetrahedrite group (such as tetrahedrite-(Fe), tetrahedrite-(Zn), tennantite), as well as with other black, metallic sulfides and sulfosalts, such as sphalerite, galena, or chalcopyrite. It differs from sphalerite by its black streak (sphalerite has a light streak), and from galena by the lack of distinct cleavage and lower density. Final distinction within the tetrahedrite group requires chemical composition analysis (e.g., by EDS method). ## Crystal Forms Crystals most often occur as tetrahedra, often with modifications of other faces. They can form twins. It also occurs in granular, massive aggregates or as inclusions in other minerals.

Geological environment

## Genesis Tetrahedrite-(Mn) forms in low- to medium-temperature hydrothermal ore veins. It is an accessory mineral in polymetallic deposits, often associated with precious metals. ## Mineral Associations It most commonly co-occurs with other sulfides and sulfosalts, such as pyrite, chalcopyrite, sphalerite, galena, tennantite, as well as with quartz, barite, dolomite, and other vein minerals. ## Localities As a member of the tetrahedrite group, it is a widely distributed mineral, but specimens specifically identified as tetrahedrite-(Mn) are much rarer. Confirmed occurrences include the Uchucchacua mine in Peru (an important locality), the Casapalca mine in Peru, as well as localities in Bulgaria, Japan (Akenobe mine), and Sweden (Garpenberg mine).

Rarity

Rare

For collectors

## Quality Criteria For collectors, well-formed, sharp, and lustrous crystals are most desirable, especially those with a distinct tetrahedral shape. Specimens where tetrahedrite-(Mn) crystals are embedded on a contrasting matrix (e.g., on white quartz or pink rhodochrosite) are highly valued. Crystal size, lack of damage, and attractive associations with other minerals (e.g., with hübnerite in the case of Peruvian specimens) significantly increase collectible value. ## Popular Localities The most known and prized tetrahedrite-(Mn) specimens by collectors come from the Uchucchacua mine in Oyon Province, Peru. They are characterized by exceptionally well-formed crystals, often in association with rhodochrosite, alabandite, and other manganese minerals.

Care and storage

## Cleaning Specimens should only be dry-cleaned, using a soft brush to remove dust. Compressed air can also be used from a safe distance. Avoid water and chemical agents. ## What to Avoid Tetrahedrite-(Mn) is sensitive to moisture and oxidation, which can lead to its slow decomposition and the formation of secondary minerals on the surface. Avoid contact with water, acids, detergents, and other chemicals. It should not be heated or exposed to sudden temperature changes. ## Storage It is recommended to store specimens in a dry environment, preferably in sealed boxes or display cases with a desiccant (e.g., silica gel). To prevent oxidation, some collectors store sensitive sulfides in an oxygen-free atmosphere.

Sources

IMA Mineral List (CNMNC)