Duranusite

Chemical formula: As₄S

Duranusite is a rare arsenic sulfide, forming small, tabular crystals with a metallic luster, found in quartz veins.

## Characteristics Duranusite is an arsenic sulfide with a metallic appearance. It typically forms very small, thin, tabular crystals, which can occur as rosetted or radial aggregates. Its color is grayish-black, and its luster is strongly metallic. Due to the small size of the crystals, its macroscopic features are difficult to observe without magnification. ## Physical Properties This mineral is very soft, with a Mohs hardness ranging from 2 to 2.5, meaning it can be scratched with a fingernail. It is opaque, but very thin fragments can be translucent dark red. It has a black streak. ## Colors and Varieties The dominant color of duranusite is grayish-black. No color or commercial varieties are distinguished. ## History and Name The mineral's name comes from the locality of Duranus in France, near which its type locality, the L'Eguisse mine, is located. It was described and recognized as a new mineral in 1973. ## Uses Due to its extreme rarity and small size, duranusite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals or systematics.

Properties

Mohs hardness
2-2.5
Luster
Metallic
Streak
Black
Density
0
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Identifying duranusite under amateur conditions is practically impossible. It requires advanced analytical methods, such as chemical composition analysis (EDS) and X-ray diffraction (XRD). Preliminary identification can be based on its co-occurrence with other arsenic minerals in known localities, metallic luster, and the form of small, tabular crystals. ## Distinguishing from Similar Minerals It can be confused with other arsenic sulfides, such as realgar or orpiment, but it differs from them in color (it is grayish-black, not red or yellow). From other gray metallic minerals (e.g., stibnite), it is distinguished by its crystal form and chemical composition. ## Crystal Forms It crystallizes in the orthorhombic system. It forms very small, thin, bladed or tabular crystals, often grouped into radial or rosetted aggregates. Crystals rarely exceed fractions of a millimeter.

Geological environment

## Genesis Duranusite is a hydrothermal mineral. It forms in low-temperature quartz-carbonate veins rich in arsenic. In its type locality, it was found in vugs within quartz veins cutting Jurassic limestones. ## Mineral Associations It co-occurs with other arsenic minerals, such as realgar, orpiment, native arsenic, as well as quartz, calcite, and dolomite. ## Localities This is an extremely rare mineral. Besides the type locality in the L'Eguisse mine near Duranus, France, its occurrence has been confirmed in only a few other places worldwide, including the Ushu mine in Kagoshima Prefecture, Japan, and the Balcooma deposit in Queensland, Australia.

Rarity

Extremely rare

For collectors

## Quality Criteria For collectors, the most important criterion is the mere presence of the mineral on the rock matrix, confirmed by analysis. Due to the microscopic size of the crystals, specimens with well-formed aggregates visible under magnification (e.g., rosettes) are most desirable. The richness of association with other rare arsenic minerals is also important. ## Popular Localities The only source of specimens of collector significance is the type locality – the L'Eguisse mine in France. Specimens from other localities are usually only available in scientific institutions.

Care and storage

## Cleaning Duranusite specimens are extremely delicate and rare. Cleaning should be kept to an absolute minimum. If necessary, compressed air can be used to remove dust. Contact with water and any chemical agents should be avoided. ## What to Avoid Avoid ultrasonic cleaners, chemicals (especially acids and bases), high temperatures, and humidity. The mineral is very soft, so it should be protected from scratches and impacts. As an arsenic sulfide, it may be sensitive to prolonged exposure to light and humid air. ## Storage Specimens should be stored in stable conditions, in a dry place, away from direct sunlight. It is best to keep them in closed collector boxes to protect them from mechanical damage and dust.

External references

Sources

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