Arsenowaylandite

Chemical formula: BiAl₃(AsO₄)₂(OH)₆

Arsenowaylandite is a rare bismuth aluminum arsenate, most commonly forming white, earthy coatings or tiny rhombohedral crystals.

## Characteristics Arsenowaylandite is a secondary mineral belonging to the arsenate group. It most often occurs as earthy, powdery, or crusty coatings on the host rock. More rarely, it forms very small, magnification-visible, rhombohedral crystals, which can form spherical or botryoidal aggregates. Its appearance is usually inconspicuous, and specimens are mainly of scientific and micromount collector interest. ## Physical Properties This mineral is characterized by a hardness in the range of 4-5 on the Mohs scale. It has an earthy or dull luster and is opaque, only translucent in very fine fragments. Its density is approximately 3.99 g/cm³. It possesses perfect cleavage in one direction. ## Colors and Varieties Arsenowaylandite is usually white, grayish-white, or yellowish-white. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1995 by a team of mineralogists (P. Ondruš, F. Veselovský, R. Skála, J. Hloušek, J. Frýda, I. Vavřín). Its name refers to its chemical composition – the dominance of arsenic (arseno-) and its structural similarity to waylandite, which is its phosphate analog. ## Uses Arsenowaylandite has no industrial application. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals and microminerals.

Properties

Mohs hardness: 4-5
Luster: Earthy
Streak: White
Density: 3.99
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Opaque to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Identifying arsenowaylandite under amateur conditions is very difficult. Clues may include its appearance (white, earthy coatings), occurrence environment (oxidation zones of ore deposits), and co-occurrence with other secondary bismuth and arsenic minerals. Definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Distinguishing from Similar Minerals Arsenowaylandite can be easily confused with its phosphate analog, waylandite, as well as with other white or yellowish secondary minerals, such as beudantite, segnitite, cerussite, or atelestite. Distinguishing them without specialized equipment is practically impossible. ## Crystal Forms Arsenowaylandite crystals are very small, with a rhombohedral habit. They usually occur as spherulitic or botryoidal aggregates, and most often as compact, earthy masses and coatings.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation (weathering) zones of polymetallic, hydrothermal ore deposits. It forms as a result of transformations of primary minerals containing bismuth and arsenic, in an aluminum-rich environment. ## Mineral Associations Arsenowaylandite often co-occurs with other secondary minerals of the oxidation zone, such as scorodite, mimetite, beudantite, segnitite, atelestite, preisingerite, as well as with relics of primary minerals, e.g., bismuthinite. ## Localities The most important occurrences of this rare mineral are in Greece (Lavrion, Attica – type locality), Germany (Clara mine in the Black Forest), Czech Republic (Jáchymov), and Switzerland (Valais canton).

Rarity

Very rare

For collectors

## Quality Criteria As a microscopic mineral, arsenowaylandite is primarily valued for the abundance of its occurrence on the matrix and for the development of small but distinct crystals forming aggregates. Specimens where it is accompanied by other rare, well-formed associated minerals are highly prized. ## Popular Localities The best specimens of this mineral are considered to be those from the Clara mine in Germany and from the historical dumps in Lavrion, Greece. Material from these localities is most sought after by micromineral collectors.

Care and storage

## Cleaning Arsenowaylandite specimens are delicate and often porous. They should only be cleaned dry, using a soft brush or a photographic air blower to remove dust. Contact with water, especially acids, can damage the mineral. ## What to Avoid Avoid ultrasonic cleaners, all chemical agents, and moisture. As an arsenate, this mineral is toxic – avoid inhaling dust and wash hands after each contact with a specimen. ## Storage It is recommended to store specimens in a dry place, preferably in closed "micromount" containers, to protect them from dust, mechanical damage, and moisture.

Sources

IMA Mineral List (CNMNC)