Arsenbrackebuschite

Chemical formula: Pb₂+₂(Fe₃+,Zn₂+)(As₅+O₄)₂(OH,H₂O)

Arsenbrackebuschite is a rare lead iron arsenate, forming small, tabular crystals with a resinous luster.

## Characteristics Arsenbrackebuschite is an arsenate belonging to the brackebuschite group. It occurs as very small, tabular or bladed crystals, rarely exceeding 1 mm in length. These crystals often form radial or irregular aggregates and clusters, as well as coatings and efflorescences on the host rock. Due to the small size of the crystals, magnification is essential for observation and identification. ## Physical Properties This mineral is characterized by a resinous luster, which on crystal surfaces approaches adamantine. It is translucent to opaque. Its Mohs hardness is approximately 4.5, and its density is quite high, which is typical for lead-bearing minerals. ## Colors and Varieties Arsenbrackebuschite exhibits colors ranging from dark red, through reddish-brown, to brown and brownish-black. Its streak, which is the color of the powdered mineral, is light brown. No varieties have been distinguished. ## History and Name The mineral was first described in 1976 by P. J. Dunn, R. C. Rouse, and J. A. Nelen. Its name refers to its structural and chemical similarity to brackebuschite and the dominance of arsenic in its composition. It was approved by the International Mineralogical Association (IMA) in the same year. The type locality (locus typicus) is the Sterling Hill Mine in Ogdensburg, New Jersey, USA. ## Uses Arsenbrackebuschite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientists.

Properties

Mohs hardness: 4.5
Luster: Resinous, Adamantine
Streak: Light brown
Density: 6.56
Cleavage: Good on {001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying arsenbrackebuschite under amateur conditions is practically impossible and requires advanced analytical methods, such as X-ray spectroscopy (EDS/WDS). Preliminary identification is based on microscopic observation of small, tabular, reddish-brown crystals with a resinous luster, occurring in the oxidation zones of polymetallic deposits, especially in association with other arsenates. ## Distinguishing from Similar Minerals Arsenbrackebuschite can be confused with many other secondary lead arsenates, such as mimetite, duftite, brackebuschite, or beudantite. Distinguishing it from brackebuschite requires confirmation of arsenic dominance over vanadium. Visually, it is almost identical to many other "brown, earthy minerals," and without chemical analysis, its certain identification is not possible. ## Crystal Forms It forms very small, thin, tabular crystals, often with a rectangular or hexagonal outline. These crystals group into rosette-like, radial, or random aggregates, and also form thin crusts and coatings.

Geological environment

## Genesis Arsenbrackebuschite is a secondary mineral, formed in the oxidation zones (gossans) of polymetallic deposits rich in lead, zinc, and arsenic. It forms as a result of weathering and alteration of primary ore minerals, such as galena, sphalerite, and arsenopyrite, under conditions of low temperatures and pressures. ## Mineral Associations This mineral co-occurs with other secondary minerals of the oxidation zone. At the type locality (Sterling Hill, USA), it was found in association with willemite, franklinite, and zincite. In Tsumeb (Namibia), it occurs with anglesite, duftite, beudantite, mimetite, and wulfenite. In other localities, it is also accompanied by goethite and quartz. ## Localities The most important and confirmed occurrences of arsenbrackebuschite are: - **USA**: Sterling Hill Mine, Ogdensburg, New Jersey (type locality). - **Namibia**: Tsumeb Mine, Oshikoto Region - known for well-formed microcrystals. - **Germany**: Clara Mine, Oberwolfach, Black Forest, Baden-Württemberg. - **Greece**: Lavrion Mines, Attica.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of arsenbrackebuschite is closely linked to the quality of its microcrystals. Most prized are specimens showing well-formed, independent, lustrous crystals of an intense, reddish-brown color, contrasting with the host rock. A rich association with other rare minerals, especially from Tsumeb or Lavrion, is also important. Crystal size, though always small, also matters – larger (above 0.5 mm) and well-formed crystals significantly increase the specimen's value. ## Popular Localities The most sought-after specimens by collectors come from the Tsumeb Mine in Namibia, which was famous for supplying the world's best microcrystals of rare minerals. Specimens from the Clara Mine in Germany and Lavrion in Greece are also valued due to the richness of their mineral associations.

Care and storage

## Cleaning Due to the small size and delicate nature of the crystals, mechanical cleaning is not recommended. If absolutely necessary, a very soft brush can be used to remove loose dust. Do not use water or any liquids that could react with the mineral or the associated rock. ## What to Avoid Avoid contact with water, acids, and other chemicals. The mineral is sensitive to shocks and impacts, which can destroy delicate crystals. It should not be heated or subjected to ultrasound. ## Storage Specimens should be stored under stable conditions, in a dry place, away from direct sunlight. The safest storage method is a sealed "micromount" box, which protects delicate crystals from mechanical damage and dust.

Sources

IMA Mineral List (CNMNC)