Moncheite

Chemical formula: Pt(Te,Bi)<sub>₂</sub>

Moncheite is a rare platinum tellurobismuthide, forming tiny, metallic inclusions in copper-nickel sulfide ores.

## Characteristics Moncheite is a mineral from the sulfide group, specifically a platinum tellurobismuthide. It typically occurs as very small, anhedral (irregularly shaped) grains or lamellar aggregates, often intergrown with other platinum-group minerals. Its size rarely exceeds 1 mm. When observed under a microscope in reflected light, it has a creamy white color with a pinkish or yellowish tint. ## Physical Properties As a metallic mineral, it is opaque and possesses a strong, metallic luster. It is quite dense, which is typical for platinum-bearing minerals. Its Mohs hardness is approximately 2-2.5, making it a soft mineral. ## Colors and Varieties Moncheite has a consistent color – in mass, it is tin-white to silvery-white. No color varieties or commercial varieties are distinguished. ## History and Name The mineral was first described in 1963 by A.D. Genkin, N.N. Zhuravlev, and E.M. Smirnova. Its name comes from its type locality – the Monchegorsk intrusion in the Murmansk Oblast on the Kola Peninsula in Russia, where it was discovered. ## Uses Moncheite, along with other platinum-group minerals, is a component of ores from which platinum and palladium are extracted. It has no direct application other than being an ore mineral. Due to the microscopic size of its crystals, it has no collector significance as a standalone specimen.

Properties

Mohs hardness: 2-2.5
Luster: Metallic
Streak: Greyish-black
Density: 10.0
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identification of moncheite is possible almost exclusively using advanced laboratory techniques, such as reflected light analysis (ore microscopy) and chemical analysis using an electron microprobe (EDS/WDS). Its high reflectance (ability to reflect light) and creamy white color are characteristic but insufficient for certain identification. ## Distinguishing from Similar Minerals It can be confused with other platinum-group minerals (PGM) such as merenskyite, kotulskite, sperrylite, or insizwaite. Differentiation requires chemical composition analysis, as all these minerals form very similar, fine, metallic grains. Moncheite is distinguished by a specific ratio of platinum, tellurium, and bismuth. ## Crystal Forms It most often forms anhedral grains and lamellae ranging from a few micrometers to about 1 millimeter in size. Poorly developed, tabular or platy crystals are rarely observed. It usually occurs as inclusions in other minerals, mainly copper and nickel sulfides.

Geological environment

## Genesis Moncheite is a mineral of magmatic origin. It forms through crystallization from residual sulfide melts in ultramafic and mafic magmatic intrusions, rich in copper and nickel. It is one of the typical platinum-group minerals in deposits of the Norilsk-Talnakh or Sudbury type. ## Mineral Associations It most commonly co-occurs with chalcopyrite, pentlandite, pyrrhotite, cubanite, and magnetite. It is also accompanied by other platinum-group minerals such as kotulskite, merenskyite, michenerite, sperrylite, as well as native metals (gold, silver). ## Localities The most important localities worldwide include: - Russia: Monchegorsk intrusion (Kola Peninsula - type locality) and deposits in the Norilsk region (Talnakh, Oktyabrskoye). - Canada: Sudbury Complex in Ontario and the Lac des Iles deposit. - South Africa: Bushveld Complex, especially in areas such as Maandagshoek farm. - Finland: Konttijärvi intrusion.

Rarity

Very rare

For collectors

## Quality Criteria Moncheite is not a mineral acquired for collecting purposes. Its value is assessed solely in the context of its platinum content in the ore. "Collector" specimens are, in practice, rock fragments or polished ore samples (ore polished sections) in which the presence of moncheite has been analytically confirmed. In such cases, the value is determined by the richness of the mineral association and the clarity of structures under the microscope, rather than the appearance of moncheite itself.

Care and storage

## Cleaning Specimens in which moncheite occurs as microscopic inclusions can be cleaned standardly, depending on the main mineral (matrix). Usually, a gentle wipe with a dry or slightly damp, soft cloth is sufficient. Ultrasonic cleaning is not recommended due to the risk of damaging the delicate matrix. ## What to Avoid Avoid contact with strong acids and chemicals that could react with the sulfide matrix or moncheite itself. As an ore mineral, it is stable under normal conditions, but it should be protected from moisture to prevent oxidation of associated minerals. ## Storage Store in a dry place, in a closed display box, to protect from dust and contaminants. Specimens with microscopic moncheite inclusions do not require special display conditions beyond standard protection from external factors.

Sources

IMA Mineral List (CNMNC)