Urancalcarite
Chemical formula: Ca(U⁶⁺O₂)₃CO₃(OH)₆·3H₂O
Urancalcarite is a rare secondary uranium mineral, forming characteristic, bright yellow, acicular crystals and radial aggregates.
Properties
- Mohs hardness
- 2-3
- Luster
- Vitreous
- Streak
- Pale yellow
- Density
- 4.03
- Transparency
- Transparent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Characteristic features of urancalcarite include its vivid yellow color, radial or stellate aggregates composed of very fine, acicular crystals, and its occurrence in paragenesis with other secondary uranium minerals. Strong radioactivity is a key diagnostic feature, easily verifiable with a Geiger counter. ## Distinguishing from Similar Minerals Urancalcarite can be confused with other yellow, secondary uranium minerals such as uranophane, becquerelite, or schoepite. Uranophane often forms similar radial aggregates but has a slightly different crystal structure and chemical composition (it is a silicate). Becquerelite forms more tabular crystals. Accurate distinction of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Crystals are elongated, acicular or bladed, developing in the orthorhombic system. They most often occur as radial, stellate, or spherulitic aggregates and crusts on the host rock.
Geological environment
## Genesis Urancalcarite is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal uraninite deposits. It forms as a result of the interaction of carbonate- and calcium-rich waters with primary uranium ores under conditions of low temperature and pressure. ## Mineral Associations It most commonly co-occurs with other secondary uranium minerals such as uranophane, becquerelite, masuyite, rutherfordine, as well as with uraninite (as a primary mineral), calcite, and gypsum. ## Localities The most important and type locality is the Shinkolobwe mine in Haut-Katanga province, Democratic Republic of Congo, from where the best-known specimens originate. It is also known from several other uranium deposit localities worldwide, though in much smaller quantities.
Rarity
Very rare
For collectors
## Quality Criteria The most prized urancalcarite specimens are those with well-formed, radial aggregates of intense, vivid yellow color, contrasting with the dark host rock (most often uraninite). The size and completeness of the aggregates, as well as the absence of damage to the delicate needles, significantly increase the collectible value of the specimen. ## Popular Localities By far the most sought-after and classic specimens come from the type locality – the Shinkolobwe mine in DR Congo. Specimens from this location are considered exemplary for this mineral species.
Care and storage
## Cleaning Urancalcarite specimens are extremely delicate and brittle. Mechanical cleaning is not recommended. If necessary, compressed air can be used from a safe distance to remove loose dust particles. Avoid contact with water and any chemicals. ## What to Avoid As a uranium mineral, urancalcarite is radioactive and requires careful handling. Direct skin contact should be avoided, and hands should be thoroughly washed after any contact. It should not be stored in areas of constant human presence (desks, bedrooms). It should be protected from moisture, high temperatures, and vibrations, which can damage the delicate crystals. ## Storage Specimens should be stored in sealed, lead-lined containers, away from other minerals that could be damaged by radiation. The container should be clearly labeled as radioactive material. It is best to store it under stable conditions, in a closed box that protects against dust and mechanical damage.