Vinciennite

Chemical formula: Cu₁₀Fe₄SnAsS₁₆

Vinciennite is a rare, metallic sulfide mineral containing copper, iron, tin, and arsenic, found in hydrothermal veins.

## Characteristics Vinciennite is a rare sulfide mineral, chemically classified as a sulfosalt. It forms very fine, anhedral (not exhibiting its own crystal form) grains, usually not exceeding 100 micrometers in size. It occurs as inclusions in other minerals, most commonly in enargite. It is opaque and has a metallic luster. ## Physical Properties This mineral is characterized by a metallic luster and a black streak. Its hardness on the Mohs scale is estimated at 4, and its density, calculated based on chemical composition and unit cell parameters, is 4.51 g/cm³. Due to the very small size of the grains, features such as cleavage or fracture have not been observed. ## Colors and Varieties Vinciennite in reflected light (under a ore microscope) is gray with a slight reddish or purplish tint. No varieties have been distinguished. ## History and Name The mineral was discovered in the La Rochette mine in the Savoie department, France. Its name honors Henri Vincienne (1898–1975), a French mining geologist who first observed this mineral in the 1950s. It was formally described and approved as a new mineral species by the International Mineralogical Association (IMA) in 1983. ## Uses Due to its extreme rarity and occurrence only as microscopic grains, vinciennite has no industrial applications. It is of purely scientific interest and is an object of interest for specialized collectors of rare minerals.

Properties

Mohs hardness: 4
Luster: Metallic
Streak: Black
Density: 4.51
Cleavage: None
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of vinciennite 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. Visual identification, even under a microscope, is practically impossible without these analyses. ## Distinguishing from Similar Minerals Under an ore microscope, vinciennite can be confused with other gray sulfosalts, such as tetrahedrite, tennantite, or even enargite, in which it often occurs. Differentiation is based on subtle differences in color tint in reflected light and on hardness, but chemical composition analysis is decisive. ## Crystal Forms Vinciennite occurs exclusively as anhedral, irregular grains dispersed within the mass of other minerals, mainly enargite. No euhedral, well-formed crystals have been observed.

Geological environment

## Genesis Vinciennite is a hydrothermal mineral. It forms in ore veins, crystallizing from solutions rich in copper, iron, tin, arsenic, and sulfur. In its type locality (La Rochette), it is associated with tin-copper mineralization. ## Mineral Associations This mineral most commonly occurs in paragenesis with enargite, luzonite, stannoidite, mawsonite, pyrite, chalcopyrite, tennantite, tetrahedrite, cassiterite, and quartz. ## Localities Beyond its type locality in the La Rochette mine (Savoie department, France), vinciennite has been identified in several other locations worldwide, including the Chinkuashih mine in Taiwan and the Uchinotai deposit in Akita Prefecture, Japan. All these occurrences are microscopic in nature.

Rarity

Very rare

For collectors

## Quality Criteria Since vinciennite occurs exclusively as microscopic inclusions, its collector value is linked to the quality of the entire specimen and the confirmed presence of the mineral. The most valuable samples are those from the type locality (La Rochette, France) with a rich association of other rare minerals, on which vinciennite has been identified by chemical analysis. The specimen itself does not possess aesthetic qualities, and its value is purely scientific and systematic. ## Popular Localities The only source of specimens of significance to collectors is the historic type locality – the La Rochette mine in France. Specimens from this mine are highly sought after by collectors specializing in rare minerals and minerals from specific localities (so-called "locality collectors").

Care and storage

## Cleaning Specimens containing microscopic vinciennite should be handled with extreme care, cleaning them only with compressed air to remove dust. Any contact with water or chemical agents is inadvisable, as it can damage both vinciennite itself and its accompanying, often sensitive, sulfides. ## What to Avoid Avoid contact with chemicals, especially acids, which can react with sulfides. This mineral, like other sulfides, can be sensitive to moisture and oxidation in the long term. It should be protected from humid air and sudden temperature changes. ## Storage Specimens with vinciennite are best stored in closed, dry containers (e.g., "perky boxes") away from direct sunlight and heat sources. Stable conditions will help preserve the original state of the mineral and its associated assemblage.

Sources

IMA Mineral List (CNMNC)