Tennantite-(Mn)

Chemical formula: Cu₁+₆(Cu₁+₄Mn₂+₂)As₃+₄S₂-₁₃

Tennantite-(Mn) is a rare mineral from the tennantite group, a copper manganese arsenosulfide, distinguished by the presence of manganese as the dominant divalent metal.

## Characteristics Tennantite-(Mn) is a rare member of the tennantite group, belonging to the tetrahedrite family. Chemically, it is a complex sulfide of copper, manganese, and arsenic. It occurs as embedded, poorly formed crystals with a tetrahedral habit, reaching sizes up to 1 mm. Most often, it forms granular and massive aggregates, intergrown with other ore minerals. Its color is steel-gray to black, and on a fresh surface, it exhibits a metallic luster. ## Physical Properties This mineral is characterized by a metallic luster and is opaque. Its Mohs hardness ranges from 3 to 4, classifying it as a relatively soft mineral. The density is significant, typical for ore minerals, and is approximately 4.85 g/cm³. ## Colors and Varieties Tennantite-(Mn) has a uniform, steel-gray to black color. No color varieties or commercial varieties are distinguished for it. Its name indicates a specific chemical composition with a dominance of manganese, which distinguishes it from other minerals in the tennantite group, such as tennantite-(Zn), tennantite-(Fe), or tennantite-(Cd). ## History and Name The mineral's name, approved by the International Mineralogical Association (IMA) in 2018, refers to its chemical composition. It is an analog of tennantite, in which manganese (Mn) is the dominant divalent element in a specific position in the crystal structure. It was first identified and described based on material from the Uchucchacua mine in Peru. ## Uses Due to its extreme rarity, tennantite-(Mn) has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of systematic and rare minerals.

Properties

Mohs hardness: 3-4
Luster: Metallic
Streak: Black
Density: 4.85
Cleavage: None
Fracture: Uneven to conchoidal
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identifying tennantite-(Mn) is extremely difficult and impossible without advanced analytical methods. Visually, it is indistinguishable from other black, metallic sulfides, especially those from the tetrahedrite group. Definitive identification requires chemical analysis (e.g., using an electron microprobe - EDS/WDS) to confirm the dominance of manganese over other divalent metals (zinc, iron) and arsenic over antimony. ## Distinguishing from Similar Minerals Tennantite-(Mn) can be confused with numerous minerals, such as other tennantites (with zinc, iron), tetrahedrites, enargite, sphalerite, or chalcopyrite. Differentiation relies solely on chemical composition analysis. Tetrahedrites contain antimony instead of arsenic, and other tennantites contain zinc, iron, or cadmium in place of manganese. ## Crystal Forms Crystals are very rare, poorly formed, and microscopic in size, usually tetrahedral in shape. Most often, it occurs as granular aggregates, massive forms, or as inclusions in other ore minerals.

Geological environment

## Genesis Tennantite-(Mn) forms in medium- and low-temperature hydrothermal deposits. It crystallizes in ore veins from solutions rich in copper, arsenic, sulfur, and manganese. ## Mineral Associations This mineral coexists with other sulfides and sulfosalts. In its type locality (Uchucchacua, Peru), it was found in association with pyrite, chalcopyrite, sphalerite, galena, quartz, alabandite, rhodochrosite, and other minerals from the tetrahedrite group. ## Localities The only confirmed and scientifically described locality for tennantite-(Mn) in the world is the Uchucchacua mine, in Oyon Province, Lima Region, Peru. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a tennantite-(Mn) specimen is primarily determined by its scientific value and the certainty of its identification. Since this mineral forms microscopic grains, the most desirable samples are those where it is visible in association with other minerals, and its presence has been confirmed by chemical analysis. Any specimen with reliable analytical documentation is extremely valuable. ## Popular Localities The only source of specimens is the Uchucchacua mine in Peru. Material from this locality is extremely rare on the collector's market and commands high prices, primarily going to institutional collections and specialized collectors of rare minerals.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to possible reactivity and the presence of arsenic, contact with water and all chemical agents should be avoided. Ultrasonic cleaning is not permitted. ## What to Avoid Avoid contact with chemicals, acids, and bases, which can damage the mineral's surface. Tennantite-(Mn) may be sensitive to prolonged exposure to humid air, which can lead to its slow oxidation and dulling. It should be protected from high temperatures and sudden changes in temperature. ## Storage It is recommended to store specimens in stable, dry conditions. Ideally, they should be placed in closed, padded collector boxes or display cases to limit air exposure and protect against mechanical damage. Due to its arsenic content, hands should be washed after handling the mineral.

Sources

IMA Mineral List (CNMNC)