Uranopilite
Chemical formula: (U<sup>6+</sup>O<sub>2</sub>)<sub>6</sub>S<sup>6+</sup>O<sub>4</sub>O<sub>2</sub>(OH)<sub>6</sub>·14H<sub>2</sub>O
Uranopilite is a secondary, bright yellow uranium mineral, forming characteristic radial aggregates and crusts in the oxidation zones of uranium deposits.
Properties
- Mohs hardness
- 2-2.5
- Luster
- Pearly
- Streak
- Yellowish
- Density
- 3.7-4.0
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification The key diagnostic feature of uranopilite is its intense yellow color and very strong, greenish-yellow fluorescence under ultraviolet light (both short- and long-wave). Its characteristic forms of occurrence as fibrous or radial aggregates and crusts are also distinctive. ## Distinguishing from Similar Minerals Uranopilite is sometimes confused with other yellow secondary uranium minerals, such as autunite, torbernite (in weathered form), uranophane, or zippeite. It differs from autunite and torbernite by the lack of distinct, tabular crystals. From uranophane, it often differs by more intense fluorescence and aggregate forms. Accurate differentiation from zippeite, with which it often co-occurs, is very difficult without advanced analyses (e.g., XRD). ## Crystal Forms Macroscopic crystals are extremely rare. Uranopilite primarily forms microcrystalline, fibrous aggregates arranged in radial rosettes, spherical aggregates, as well as dense, felt-like crusts and coatings on rocks.
Geological environment
## Genesis Uranopilite is a secondary mineral, forming in the oxidation (weathering) zones of uraninite and other primary uranium minerals. It forms as a result of sulfate-rich waters acting on uranium minerals. It is a typical product of weathering processes in uranium mines. ## Mineral Associations It most often co-occurs with other secondary uranyl sulfates and silicates. Its typical associated minerals include gypsum, johannite, uranophane, zippeite, and relics of primary uraninite. ## Localities Significant uranopilite localities worldwide include Jáchymov (Czech Republic), Schneeberg, and Johanngeorgenstadt (Germany). It also occurs in many uranium mines in the USA, especially in Utah (e.g., Delta mine), Arizona, Colorado, and New Mexico. It is also found in deposits in Canada and France.
Rarity
Not very common
For collectors
## Quality Criteria The most valued by collectors are specimens with well-formed, radial aggregates of intense, lemon-yellow color, contrasting with the dark matrix rock. The size and richness of the crusts are also important. Due to its delicacy, specimens without mechanical damage are much more highly valued. ## Popular Localities Classic and most sought-after localities include Jáchymov in the Czech Republic and historical mines in Saxony, Germany. High-quality specimens also come from some mines in Utah, USA.
Care and storage
## Cleaning Uranopilite specimens should not be wet cleaned. Only gentle dust removal with a soft brush or compressed air from a safe distance is permissible. ## What to Avoid Absolute avoidance of contact with water is necessary, as it can dissolve and destroy delicate crystals. The mineral is sensitive to changes in humidity and temperature. As a uranium mineral, it is strongly radioactive – direct skin contact, inhalation of dust, and storage in areas of constant human presence (especially bedrooms and offices) should be avoided. ## Storage Uranopilite specimens require specialized conditions. They should be stored in sealed, lead or glass containers, away from other radiation-sensitive minerals. Containers should be clearly labeled as radioactive material. Store in a dry place, preferably with a desiccant.