Arsenovanmeersscheite

Chemical formula: U<sup>6+</sup>(U<sup>6+</sup>O<sub>2</sub>)<sub>3</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>·4H<sub>2</sub>O

Arsenovanmeersscheite is a rare, secondary uranyl mineral, an arsenate variety of vanmeersscheite, forming yellow, tabular crystals.

## Characteristics Arsenovanmeersscheite is an arsenate analog of vanmeersscheite, belonging to the group of secondary uranium minerals. It occurs as small, tabular or bladed crystals, which often form rosette-like or radial aggregates. Its intense yellow color is characteristic of many uranyl minerals. ## Physical Properties The crystals are very small and brittle. The mineral exhibits strong, green fluorescence under ultraviolet light (both shortwave and longwave). It is highly radioactive, requiring special precautions. ## Colors and Varieties This mineral occurs in shades from pale yellow to golden yellow. No varieties have been distinguished. ## History and Name The name refers to its chemical composition – it is an arsenic (arseno-) analog of vanmeersscheite (-vanmeersscheite). It was described as a new mineral in 1997 by Michel Deliens and Paul Piret based on specimens found in the Shinkolobwe mine in the Democratic Republic of Congo. ## Uses Due to its rarity and small crystal size, arsenovanmeersscheite has no industrial application. It is of purely scientific and collector's interest, being an object of fascination for specialized collectors of uranium minerals.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Pale yellow
Density
4.75
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features include intense yellow color, tabular crystal habit forming characteristic aggregates, strong green fluorescence under UV light, and high radioactivity. However, identification requires specialized equipment. ## Distinguishing from Similar Minerals It can be confused with many other yellow secondary uranium minerals, such as autunite, torbernite (in meta-form), uranophane, or vanmeersscheite itself. Definitive differentiation is almost exclusively possible through chemical analysis (EDS/WDS) or X-ray diffraction (XRD), which allow for the identification of arsenic as a key component and confirmation of the crystal structure. ## Crystal Forms It forms thin, tabular crystals with a rectangular or hexagonal outline. These crystals often combine into radial, stellate, or rosette-like aggregates, and also form thin coatings and crusts on the host rock.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation (weathering) zones of uraninite deposits and other primary uranium minerals. It crystallizes from aqueous solutions rich in uranium and arsenic under low temperature and pressure conditions. ## Mineral Associations It most often co-occurs with other secondary uranium minerals, such as vanmeersscheite, kamotoite-(Y), schoepite, uranophane, as well as with primary uraninite. ## Localities The only confirmed and described locality (type locality) of this mineral is the Shinkolobwe mine in Haut-Katanga Province in the Democratic Republic of Congo. This is a historic, now inactive uranium and cobalt mine.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens are those with well-formed, sharp crystals forming aesthetic, radial aggregates on a contrasting rock matrix. Intense, pure color and lack of damage to the delicate crystals are important. Due to its rarity, any well-defined specimen is valuable. ## Popular Localities The only source of specimens is the historical type locality – the Shinkolobwe mine in the DRC. Material from this mine is available only on the secondary market, often originating from old collections.

Care and storage

## Cleaning Specimens should not be cleaned wet. Only gentle dust removal with a soft brush or compressed air from a safe distance is permissible. ## What to Avoid Contact with water and chemicals should be strictly avoided. The mineral is sensitive to changes in temperature and humidity. As a secondary mineral, it can dehydrate in overly dry environments, leading to its destruction. It is highly radioactive – direct skin contact, inhalation of dust, and storage near areas of permanent human presence should be avoided. ## Storage Specimens should be stored in sealed, lead-lined or thick-glass containers clearly marked with radioactivity warnings. It is best to keep them in stable humidity conditions, away from sunlight and heat sources.

Sources

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