Berndlehmannite

Chemical formula: Cu₂+(Cr₃+V₃+)S₂-₄

Berndlehmannite is an extremely rare, black, metallic copper, chromium, and vanadium sulfide, found in only one location worldwide.

## Characteristics Berndlehmannite is a copper, chromium, and vanadium sulfide belonging to the linnaeite group. It forms very small, individual, submetallic grains up to 200 micrometers in size. It typically occurs as inclusions within other minerals, mainly bornite and chalcocite. Its grains are most often anhedral (do not exhibit their own crystal faces). ## Physical Properties This mineral is characterized by a metallic luster and a black streak. It is opaque. Due to the microscopic size of the grains, precise determination of hardness and density was not possible. The density calculated based on the chemical formula and unit cell parameters is 4.45 g/cm³. ## Colors and Varieties Berndlehmannite is black. In reflected light under a polarizing microscope, its color is gray with a slight reddish tint. No varieties have been distinguished. ## History and Name The mineral was discovered in the Ragra copper mine in the Pasco region of Peru. It was officially approved by the International Mineralogical Association (IMA) in 2019 (IMA2019-051). The name honors Professor Berndt D. Lehmann (born 1948), a German economic geologist from Clausthal University of Technology, for his contributions to metallogenesis and the geology of ore deposits, including the Ragra deposit. ## Applications Berndlehmannite has no industrial or commercial applications. Its significance is purely scientific and collectible, as a unique and newly discovered mineral.

Properties

Luster: Metallic
Streak: Black
Density: 4.45
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of berndlehmannite is possible only through advanced laboratory methods, such as electron microprobe analysis (EDS/WDS) to determine chemical composition and X-ray diffraction (XRD) to confirm crystal structure. Macroscopic visual identification is impossible. ## Distinguishing from Similar Minerals Under a reflected light microscope, berndlehmannite can be confused with other sulfides from the linnaeite group, such as carrollite, linnaeite, or siegenite. Differentiation requires precise chemical analysis, which will show the simultaneous, significant presence of chromium and vanadium, which is unique to this mineral. ## Crystal Forms Berndlehmannite occurs as anhedral or subhedral grains, usually of irregular shape, dispersed in the matrix of other sulfides. No well-formed crystals have been observed.

Geological environment

## Genesis Berndlehmannite formed as a result of hydrothermal processes. It occurs in sulfide veins cutting through mudstones of the Goyllarisquisga Formation. Its crystallization is associated with the presence of vanadium derived from surrounding sedimentary rocks rich in organic matter. ## Mineral Associations This mineral occurs in close association with bornite, chalcocite, digenite, covellite, pyrite, sphalerite, galena, patronite, minerals from the linnaeite group, and quartz. ## Locations The only confirmed occurrence of berndlehmannite in the world is its type locality - the Ragra mine, located in the Huayllay district, Pasco province and region, Peru.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, the collector's value of berndlehmannite is not assessed based on typical criteria such as size or crystal form. The most valuable specimens are those in which the presence of berndlehmannite has been analytically confirmed. The richness of the mineral association on the specimen and the clarity and size of the grains under the microscope increase its value. ## Popular Localities The only source of specimens is the Ragra mine in Peru. Material from this locality is extremely difficult to acquire and is almost exclusively available in specialized collections and research institutions.

Care and storage

## Cleaning Specimens containing berndlehmannite should not be cleaned mechanically or chemically due to the microscopic size and fragility of the inclusions. Any attempts at cleaning may destroy or remove the mineral grains from the surrounding matrix. ## What to Avoid Avoid contact with chemicals, acids, and ultrasound. Changes in temperature and humidity can affect the stability of the surrounding sulfides (mainly bornite), which may lead to damage to the specimen. ## Storage Specimens should be stored under stable conditions, in a closed display box, to protect them from dust, mechanical damage, and sudden environmental changes. Due to its microscopic nature, it is best stored in a special "micromount" box.

Sources

IMA Mineral List (CNMNC)