Calciouranoite
Chemical formula: (Ca,Ba,Pb<sup>2+</sup>,K,Na)U<sup>6+</sup><sub>2</sub>O<sub>7</sub>·5H<sub>2</sub>O
Calciouranoite is a rare, secondary uranium mineral with an intensely orange color, occurring in the oxidation zones of uranium deposits.
Properties
- Mohs hardness
- 2-3
- Luster
- Dull
- Streak
- Orange-yellow
- Density
- 4.69
- Cleavage
- Perfect on {100}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The key diagnostic feature of calciouranoite is its intense orange color, its occurrence in the form of radial or earthy aggregates, and its strong radioactivity, easily detectable with a Geiger-Müller counter. It occurs in a characteristic geological environment - the oxidation zones of uranium deposits. ## Distinguishing from Similar Minerals It can be confused with other secondary uranium minerals of similar color, such as becquerelite or curite. Becquerelite has a similar composition but crystallizes in the orthorhombic system and often forms better-developed crystals. Curite (uranium and lead oxide) has a higher density. Reliable distinction of these minerals is possible almost exclusively using advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms microscopic, platy or acicular crystals, rarely exceeding fractions of a millimeter. It is most often observed in the form of radial aggregates, rosettes, fibrous masses, as well as earthy and powdery coatings and crusts on other minerals.
Geological environment
## Genesis Calciouranoite is a secondary mineral, formed in the oxidation (weathering) zones of hydrothermal uranium deposits. It forms as a result of the alteration of primary uranium minerals, mainly uraninite, under the influence of calcium-rich waters. ## Mineral Associations It most often co-occurs with uraninite (as a primary mineral), as well as with other secondary uranium minerals such as becquerelite, schoepite, curite, kasolite, uranophane, and gypsum. ## Localities The most important and classic localities for this mineral are the Mounana deposit in Gabon and Shinkolobwe in the Democratic Republic of Congo. It is also known from several places in Germany (e.g., the Krunkelbach mine in the Black Forest) and from Utah in the USA.
Rarity
Very rare
For collectors
## Quality Criteria The most valued by collectors are specimens with rich, well-formed, radial aggregates of intense orange color. Contrast with the rock matrix and the presence of associated minerals are also important. Due to the microscopic nature of the crystals, the size of individual needles is not a key criterion - the overall aesthetics and richness of the entire aggregate are what count. ## Popular Localities Specimens from historical localities, such as Mounana in Gabon and Shinkolobwe in the DRC, are considered classics and are highly sought after. High-quality micromounts also come from German localities.
Care and storage
## Cleaning The mineral is extremely delicate and brittle. It should not be cleaned mechanically or chemically. Any attempts at cleaning may lead to irreversible damage to the specimen. Only very careful removal of loose contaminants with a soft brush or a photographic air blower is permissible. ## What to Avoid Contact with water, chemicals, ultrasound, and sudden temperature changes must be strictly avoided. As a strongly radioactive mineral, it requires special precautions. Direct skin contact, inhalation of dust, and storage in places of permanent human presence should be avoided. ## Storage Calciouranoite specimens must be stored in sealed, lead-lined containers or specialized thick plastic display cases, away from other radiation-sensitive minerals. The container must be clearly marked with a radioactivity symbol. Store in a dry place, away from sources of light and heat.