Roubaultite

Chemical formula: Cu²⁺₂O₂(U⁶⁺O₂)₃(CO₃)₂(OH)₂·4H₂O

Roubaultite is a very rare, secondary uranyl and copper mineral, forming characteristic, tabular crystals of an intense green color.

## Characteristics Roubaultite is a complex hydrated uranyl and copper hydroxycarbonate. It occurs as very small, tabular or bladed crystals, which rarely exceed 1 mm in length. These crystals often form rosette-like or radial aggregates, as well as thin coatings and crusts on the host rock. Its intense, emerald-green color is very characteristic. ## Physical Properties This mineral is characterized by a Mohs hardness of approximately 3. It has perfect cleavage in one direction, which accounts for its tabular appearance. The luster is vitreous, and on cleavage surfaces, it can be pearly. It is a relatively dense mineral, which is typical for uranium minerals. ## Colors and Varieties Roubaultite occurs in a uniform, emerald-green color. No color varieties or commercial varieties are known. ## History and Name The mineral was first described in 1971 by Fabien Cesbron, R. Pierrot, and T. Verbeek. The name was given in honor of Marcel Roubault (1905-1974), a French geologist and professor at the University of Nancy, specializing in the geology of uranium deposits. ## Uses Due to its extreme rarity and small crystal size, roubaultite has no industrial applications. It is solely an object of interest for collectors specializing in uranium minerals and rare mineral species.

Properties

Mohs hardness
3
Color
Grass-green to apple-green
Luster
Vitreous, Pearly
Streak
Light green
Density
0
Cleavage
Perfect on {100} and imperfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Key diagnostic features of roubaultite include its characteristic emerald-green color, tabular crystal habit, formation of rosette-like aggregates, and occurrence in the oxidation zones of uranium deposits. The mineral exhibits strong, green fluorescence under ultraviolet light (both shortwave and longwave). It is also highly radioactive, which can be easily detected with a Geiger counter. ## Distinguishing from Similar Minerals Roubaultite can be confused with other green secondary copper and uranium minerals, such as cuprosklodowskite, torbernite, or zeunerite. It differs from cuprosklodowskite by its crystal habit (tabular instead of acicular). It is distinguished from torbernite and zeunerite by its habit (rosette-like aggregates of blades instead of square tablets) and crystallographic system (triclinic, not tetragonal). ## Crystal Forms Crystals are usually very small, flattened, with a tabular or bladed habit, elongated in one direction. They often combine into radial or rosette-like aggregates, and also form fan-shaped clusters.

Geological environment

## Genesis Roubaultite is a secondary mineral formed in the oxidation (weathering) zones of hydrothermal uranium deposits rich in copper. It forms as a result of the action of waters containing dissolved oxygen, carbonates, and copper on primary uranium minerals, such as uraninite. ## Mineral Associations This mineral co-occurs with other secondary uranium and copper minerals. It is most commonly found in association with uraninite (as a primary mineral) and cuprosklodowskite, vandenbrandeite, torbernite, malachite, and quartz. ## Localities The most important and type locality for roubaultite is the Shinkolobwe mine in Haut-Katanga Province, Democratic Republic of Congo, from which the best known specimens originate. This is the only locality where this mineral occurs in quantities allowing for the collection of collector specimens.

Rarity

Very rare

For collectors

## Quality Criteria The most valued roubaultite specimens are those with well-formed, sharply terminated crystals forming aesthetic, rosette-like or fan-shaped aggregates. The intensity and purity of the emerald-green color also significantly increase the specimen's value. Contrast with the light host rock and the absence of damage to the delicate crystals are also important. Due to the microscopic size of the crystals, specimens are primarily evaluated under magnification. ## Popular Localities The only source of valuable collector-grade roubaultite specimens is the historic Shinkolobwe mine in the Democratic Republic of Congo. Specimens from this locality are considered classic and most desired by collectors specializing in systematic and uranium minerals.

Care and storage

## Cleaning Roubaultite specimens are extremely delicate and fragile. Cleaning should be limited to an absolute minimum. If necessary, a very soft brush can be used to remove loose dust particles. Contact with water and any chemical agents should be avoided. ## What to Avoid Roubaultite is a uranium mineral and is radioactive. Direct, prolonged skin contact should be avoided, and above all, inhalation of dust or mineral particles. It should not be heated or exposed to acids. Specimens should be protected from moisture and vibrations. ## Storage It is recommended to store specimens in sealed, transparent containers (so-called micromount boxes), which protect them from mechanical damage and dust, and also limit radon emission. These containers should be clearly labeled as containing radioactive material. They should be kept away from areas of permanent human presence, especially bedrooms and living rooms.

External references

Sources

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