Metavanmeersscheite

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

Metavanmeersscheite is a rare, secondary uranyl mineral, forming characteristic yellow, platy crystals and radial aggregates.

## Characteristics Metavanmeersscheite is a hydrated uranyl phosphate, belonging to the group of secondary minerals found in the oxidation zones of uranium deposits. It forms very small, thin, platy crystals with a hexagonal outline, which often combine into rosette-like or radial aggregates. Due to its chemical composition, this mineral is strongly radioactive. ## Physical Properties Metavanmeersscheite crystals exhibit a vitreous luster. They are brittle and have perfect cleavage in one direction, parallel to the plane of the plates. The Mohs hardness is approximately 2, and the density is estimated at 4.7 g/cm³. ## Colors and Varieties This mineral occurs in a characteristic, bright yellow color. No color or commercial varieties are distinguished. ## History and Name Metavanmeersscheite was first described in 1986 by Michel Deliens and Paul Piret. Its name refers to its close structural relationship with the mineral vanmeersscheite, from which it differs by a lower degree of hydration (the prefix "meta-" indicates a lower water content). The name of the parent mineral honors the Belgian crystallographer Maurice Van Meerssche (1923-1988). ## Uses Due to its rarity, small crystal size, and strong radioactivity, metavanmeersscheite has no industrial applications. It is solely an object of interest for collectors specializing in uranium minerals and scientists.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Pale yellow
Density
4.7
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features include its bright yellow color, characteristic form of thin, platy crystals forming radial aggregates, and strong radioactivity. The mineral also exhibits strong, green fluorescence under ultraviolet light (both shortwave and longwave). ## Distinguishing from Similar Minerals Metavanmeersscheite is visually almost identical to vanmeersscheite. Distinguishing these two minerals is only possible using advanced analytical methods, such as X-ray diffraction (XRD), which allow for the determination of the degree of hydration. It can also be confused with other secondary uranyl minerals, such as autunite or torbernite, but often differs from them in crystal habit and hue. ## Crystal Forms Crystals are very thin, platy, with a hexagonal outline. They most often occur as radial or rosette-like clusters and aggregates, as well as coatings and efflorescences on the host rock.

Geological environment

## Genesis Metavanmeersscheite is a secondary mineral, formed in the oxidation (weathering) zones of hydrothermal uraninite deposits. It forms as a result of the alteration of primary uranium ores under the influence of phosphate-rich waters. ## Mineral Associations It most often co-occurs with the mineral from which it derives its name – vanmeersscheite. It is also accompanied by other secondary uranium minerals, such as studtite, rutherfordine, schoepite, as well as quartz and clay minerals. ## Localities The only known and confirmed locality for this mineral in the world is the Shinkolobwe uranium mine in Haut-Katanga Province, Democratic Republic of Congo. This is the so-called type locality (place of discovery).

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens are those with well-formed, radial aggregates of an intense yellow color, contrasting with the dark host rock (most often uraninite). The size of the aggregates and the absence of mechanical damage significantly increase collectible value. Due to the microscopic size of the crystals, specimens are usually small. ## Popular Localities The only source of metavanmeersscheite specimens is the Shinkolobwe mine in the DRC. This mine is currently closed and inaccessible, making material from this locality historical and very difficult to obtain on the collector's market.

Care and storage

## Cleaning Specimens should not be wet cleaned. A soft brush or compressed air from a safe distance can be used to remove dust. Avoid contact with water, which can damage delicate crystals. ## What to Avoid The mineral is strongly radioactive – limit exposure and always wash hands after contact. Avoid inhaling dust. Do not heat the specimen, as this may lead to further dehydration and its destruction. Protect from chemicals and moisture. ## Storage Store in a sealed, lead-lined or thick-glass container, away from other radiation-sensitive minerals. The container should be clearly labeled as radioactive material. Keep in a dry place, away from areas of permanent human presence.

Sources

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