Černýite

Chemical formula: Cu₁+₂Cd₂+Sn₄+S₂-₄

Černýite is a rare, metallic sulfide mineral containing copper, cadmium, and tin, forming tiny grains embedded in other minerals.

## Characteristics Černýite is a rare sulfide mineral belonging to the stannite structural group. It typically occurs as anhedral (irregularly shaped) grains, which are embedded in other sulfide minerals, mainly kesterite and sphalerite. Its size rarely exceeds 0.5 mm. Macroscopically, it is indistinguishable from the surrounding sulfides. In polished sections under a reflected light microscope, it exhibits a gray color with a slight pinkish or brownish tint. ## Physical Properties Due to its occurrence in very fine grains, most physical properties are difficult to determine precisely. Its Mohs hardness is estimated at approximately 4. The mineral is opaque and exhibits a metallic luster. The density calculated based on its chemical formula and unit cell parameters is 4.96 g/cm³. ## Colors and Varieties Černýite has a steel-gray color, often with a subtle hue. No color varieties or commercial varieties are known. ## History and Name The mineral was discovered in the Tanco Mine in Bernic Lake, Manitoba, Canada. It was described in 1978 by a team of mineralogists: L.J. Kissin, T.T. Chen, W.D. Gunter, and J.D. Grice. The name "černýite" was given in honor of Dr. Petr Černý (1934–2018), a Czech-Canadian mineralogist from the University of Manitoba, in recognition of his contributions to pegmatite mineralogy, including the Tanco pegmatite where the discovery was made. ## Uses Černýite has no industrial application. It is of purely scientific interest and is an object of interest for collectors specializing in rare systematic minerals.

Properties

Mohs hardness: 4
Color: Steel Grey
Luster: Metallic
Streak: Black
Density: 4.76
Cleavage: Imperfect on {112}
Fracture: Uneven
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of černýite is impossible without advanced laboratory techniques. It requires analysis by reflected light microscopy (optical analysis in a polished section) and confirmation of chemical composition using an electron microprobe (EDS/WDS) or X-ray diffraction (XRD). Under collecting and field conditions, it is unrecognizable. ## Distinguishing from Similar Minerals Černýite is visually almost identical to other minerals from the stannite group, such as kesterite, stannite, kuramite, and hocartite, with which it often co-occurs. Definitive differentiation is possible only through chemical analysis, which allows for the precise determination of copper, cadmium, tin, zinc, and iron proportions. ## Crystal Forms This mineral forms only irregular, anhedral grains and aggregates. No well-formed crystals have been observed.

Geological environment

## Genesis Černýite is a hydrothermal mineral, crystallizing in the late stages of the evolution of complex lithium-cesium-tantalum (LCT-type) granitic pegmatites. It forms in sulfide-mineralized zones where tin and cadmium become concentrated. ## Mineral Associations This mineral most commonly co-occurs with kesterite, sphalerite, stannite, chalcopyrite, kuramite, and hocartite. It is also accompanied by other pegmatite minerals such as quartz, spodumene, tantalite, and pollucite. ## Localities The most important and well-documented localities of černýite worldwide include: - Type locality: Tanco Mine in Bernic Lake, Manitoba, Canada. - Hugo Mine, Pennington County, South Dakota, USA. - Kutessay II deposit in the Chüy Region, Kyrgyzstan. - Various pegmatites in the Kaatiala region, Finland.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a černýite specimen is not assessed based on visual criteria such as color or luster, as the mineral is microscopic. The highest value is placed on specimens where the presence of černýite has been analytically confirmed (e.g., by electron microprobe), and the grains are relatively large (for this mineral, e.g., 0.1-0.5 mm) and clearly visible in the matrix. The reliability of the locality and accompanying analytical documentation are crucial. ## Popular Localities Specimens from the type locality – the Tanco Mine in Canada – are most prized by specialist collectors. Material from other confirmed localities, such as South Dakota or Kyrgyzstan, is also sought after due to the extreme rarity of the mineral.

Care and storage

## Cleaning Specimens containing černýite, due to their nature (tiny inclusions in other minerals), generally do not require and should not undergo mechanical or chemical cleaning. Any attempt at isolation or cleaning risks destroying the microscopic grains. It is best to leave the specimen undisturbed. ## What to Avoid Avoid contact with chemicals, acids, and bases that may react with sulfides. Also, avoid ultrasonics and sudden temperature changes. Prolonged exposure to humid air can lead to slow surface oxidation. ## Storage Specimens with černýite are best stored under stable conditions, in a closed display box, protecting them from dust, moisture, and chemical contamination. Due to the microscopic nature of the mineral, proper and permanent labeling of the specimen along with the precise location of the černýite grains is crucial.

External references

https://www.mindat.org/min-1210.html