Stibarsen

Chemical formula: SbAs

Stibarsen is a natural alloy of antimony and arsenic, forming granular or massive aggregates with a metallic luster, often covered with a gray patina.

## Characteristics Stibarsen, also known as allemontite, is a natural alloy (intermetallic compound) of antimony and arsenic. It rarely forms distinct crystals, most often occurring as compact, granular, reniform, or crust-like aggregates. Freshly fractured surfaces are tin-white or reddish-gray and exhibit a strong metallic luster, but they quickly tarnish and become covered with a gray or black patina upon exposure to air. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3-4. It is characterized by a metallic luster and is opaque. Its density is significant, approximately 5.8 g/cm³, which makes specimens heavy for their size. It also exhibits perfect cleavage in one direction. ## Colors and Varieties Typical colors of stibarsen are tin-white and reddish-gray on fresh surfaces. Over time, it oxidizes, turning from gray to black. The name allemontite is sometimes used to refer to mixtures of stibarsen with native arsenic or antimony, but it is not a distinct variety in the mineralogical sense. ## History and Name The name "stibarsen" is a portmanteau of the Latin names of its constituent elements: *stibium* (antimony) and *arsenicum* (arsenic). The mineral was formally described and named in 1941. Its type locality is the Varuträsk pegmatite in Sweden. ## Uses Stibarsen has no significant industrial applications. It is valued primarily by collectors specializing in native elements and intermetallic compounds.

Properties

Mohs hardness: 3-4
Luster: Metallic
Streak: Gray
Density: 5.8
Cleavage: in one direction
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Stibarsen can be identified by its high density, metallic luster on a fresh fracture, and the characteristic gray or black patina on weathered surfaces. Its relatively low hardness (3-4 on the Mohs scale) is also a helpful feature. ## Distinguishing from Similar Minerals It can be confused with native arsenic or native antimony. Pure arsenic usually has a more tin-white color and a granular structure. Pure antimony is more silvery-white and has more distinct cleavage. Accurate differentiation of these three substances often requires chemical analysis (EDS). ## Crystal Forms Well-formed crystals are extremely rare. Stibarsen most often forms massive, granular, reniform, or radial aggregates. It also occurs as dendritic or skeletal forms embedded in calcite.

Geological environment

## Genesis Stibarsen forms under hydrothermal conditions, most often in medium- to low-temperature ore veins. It is also found in some granitic pegmatites, where it crystallizes with other rare minerals. ## Mineral Associations It often co-occurs with native arsenic, native antimony, native bismuth, as well as with minerals such as calcite, quartz, barite, and various sulfides and arsenides (e.g., arsenopyrite, loellingite). ## Localities Important worldwide localities include Allemont in France (hence the historical name allemontite), the St Andreasberg mine in the Harz Mountains in Germany, Varuträsk in Sweden (type locality), Příbram in the Czech Republic, and Atlin in British Columbia, Canada.

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, though rare, crystalline forms or interesting dendritic aggregates are most valued by collectors. The presence of a fresh, unoxidized surface with a strong luster, often in contrast to the natural patina, is also important. Large, massive pieces also have collector value. ## Popular Localities Classic and most sought-after specimens come from historical European localities such as Allemont in France and St Andreasberg in Germany. Specimens from Atlin, Canada, known for dendritic forms in calcite, are also highly prized in the collector's market.

Care and storage

## Cleaning Stibarsen specimens should only be dry-cleaned, using a soft brush to remove dust. Contact with water, and especially with chemicals, can accelerate the oxidation process and damage the mineral's surface. ## What to Avoid Moisture, acids, detergents, and ultrasonic cleaners should be strictly avoided. The mineral is sensitive to air, which causes it to darken (patinate). Do not attempt to chemically remove the natural patina, as this may damage the specimen. ## Storage It is recommended to store stibarsen in dry, airtight containers (e.g., membrane boxes or boxes with a desiccant) to limit its contact with air and moisture. It should be kept away from other minerals that it could scratch or that could damage it.