Viaeneite

Chemical formula: (Fe²⁺,Pb²⁺)₄((S₂)²⁻,S⁶⁺)₈O

Viaeneite is a rare iron and lead sulfide, forming microscopic, black, metallic grains in sediments from coal dump fires.

## Characteristics Viaeneite is a sulfide mineral, occurring as very fine, irregular grains, usually not exceeding 100 micrometers in size. It forms granular aggregates and massive masses. It is opaque and has a black color with a metallic luster. Due to the microscopic size of its crystals, its macroscopic features are difficult to observe without specialized equipment. ## Physical Properties This mineral is characterized by a metallic luster and a black streak. Its hardness and density have not been precisely determined due to the small size of the samples. It is brittle. ## Colors and Varieties Viaeneite occurs exclusively in black. No varieties have been distinguished. ## History and Name The mineral is named in honor of Professor Willy Viaene (1940-1990), a Belgian geologist from the Catholic University of Leuven, in recognition of his contributions to ore deposit research. It was approved as a new mineral by the International Mineralogical Association (IMA) in 1994. The type locality is near the town of Aniche in northern France. ## Applications Due to its rarity and microscopic size, viaeneite has no industrial applications and is solely an object of scientific interest and a collector's item for specialized microscopic mineral collectors.

Properties

Mohs hardness
3.5-4.5
Color
Yellow
Luster
Metallic
Streak
Black
Density
3.8
Cleavage
On {110}
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of viaeneite is possible only through advanced laboratory methods, such as chemical analysis (EDS) and X-ray diffraction (XRD). In collector's conditions, identification relies on a label from a confirmed locality. Visually, it appears as black, metallic, microscopic grains. ## Distinguishing from Similar Minerals It can be confused with other black, metallic sulfides found in similar environments, such as pyrite or marcasite. Differentiation requires specialized studies, as viaeneite does not form characteristic crystal forms visible under an optical microscope. ## Crystal Forms Viaeneite forms only anhedral (irregularly shaped), irregular grains and massive, granular aggregates. No well-formed crystals have been observed.

Geological environment

## Genesis Viaeneite is an anthropogenic mineral. It forms as a result of processes occurring in self-ignited coal dumps. It forms in high-temperature zones under reducing conditions, through reactions between sulfide minerals and organic matter contained in mining waste. ## Mineral Associations It co-occurs with other minerals typical of burning dump environments, such as native sulfur, sal ammoniac, realgar, orpiment, as well as various sulfates and oxides formed under these specific conditions. ## Localities The most important and well-documented occurrences of this mineral are in Europe. It was discovered in coal dumps in Aniche, Nord department, France (type locality). It is also known from dumps in the Kladno region in the Czech Republic and from burning dumps in Pennsylvania (USA).

Rarity

Very rare

For collectors

## Quality Criteria The quality of a viaeneite specimen is primarily assessed based on the richness of the aggregates and the size of individual grains, although these rarely exceed fractions of a millimeter. The most prized samples are those where black, metallic aggregates of viaeneite form a clear contrast with the lighter host rock. Certainty of identification from a reputable laboratory and precise locality are also crucial. ## Popular Localities The most classic and sought-after specimens by collectors come from the type locality in Aniche, France. Material from Czech dumps in the Kladno region is also found in specialized collections.

Care and storage

## Cleaning Viaeneite specimens are typically microscopic and embedded in a rock matrix. Cleaning is not recommended, as it can easily damage or dislodge the delicate mineral grains. Any attempts at cleaning should be limited to very careful dust removal using compressed air from a safe distance. ## What to Avoid Avoid contact with chemicals, acids, and washing in water, especially with ultrasonics. The mineral may be sensitive to rapid changes in temperature and humidity, which can lead to its decomposition. Protect it from direct sunlight. ## Storage Microscopic specimens should be stored in specialized "micromount" boxes, which protect them from dust, mechanical damage, and humidity changes. Store in stable room conditions, away from heat and light sources.

External references

Sources

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