Widenmannite
Chemical formula: Pb<sup>2+</sup><sub>2</sub>U<sup>6+</sup>O<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>2</sub>
Widenmannite is a rare, secondary uranyl lead mineral, forming characteristic yellow coatings and aggregates of fine crystals.
Properties
- Mohs hardness
- 3-4
- Luster
- Vitreous to silky
- Streak
- Light yellow
- Density
- 6.5
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Key diagnostic features include its intense yellow color, occurrence as fine, acicular or platy crystals forming radial aggregates, and strong yellow fluorescence under UV light. High density is also a helpful characteristic. ## Distinguishing from Similar Minerals Widenmannite can be confused with other yellow secondary uranium minerals such as boltwoodite, uranophane, or kasolite. Differentiation often requires advanced analytical methods (e.g., XRD, EDS), although the characteristic radial aggregate form and flexibility of the crystals can be helpful in visual identification. ## Crystal Forms Crystals are elongated, platy, or acicular, often flattened. They typically form radial, stellate, or spherulitic aggregates, as well as thin coatings and crusts.
Geological environment
## Genesis Widenmannite is a secondary mineral, formed in the oxidation (weathering) zones of hydrothermal uranium deposits that also contain lead sulfides, mainly galena. It forms as a result of carbonate-rich waters acting on primary uranium and lead minerals. ## Mineral Associations It most often co-occurs with other secondary uranium and lead minerals, such as boltwoodite, uranophane, kasolite, fourmarierite, as well as galena, uraninite, fluorite, quartz, and barite. ## Localities The most important localities worldwide include the discovery site – the Michael mine in Wittichen (Black Forest, Germany), as well as the Uranus mine in Kleinrückerswalde near Annaberg-Buchholz (Saxony, Germany). It is also known from several other localities in Germany, France (Margnac deposit), and the Czech Republic.
Rarity
Very rare
For collectors
## Quality Criteria Specimens with well-formed, distinct radial aggregates or spherulites of intense yellow color, contrasting with the dark host rock, are most valued by collectors. The size and richness of the aggregates on the matrix are key factors influencing the value of a specimen. ## Popular Localities Specimens from classic German localities, such as the Michael mine in the Black Forest or the Uranus mine in Saxony, are considered the most desirable due to their historical significance and quality.
Care and storage
## Cleaning Widenmannite specimens are extremely delicate and fragile. Mechanical cleaning should be avoided. If absolutely necessary, compressed air (from a safe distance) can be used to remove dust. Contact with water is not recommended, as it can damage the fine crystals. ## What to Avoid Contact with acids and other chemicals must be strictly avoided. The mineral is sensitive to changes in temperature and humidity. As a radioactive mineral, it requires careful handling – avoid inhaling dust and wash hands after each contact. ## Storage Specimens should be stored in closed, airtight containers (e.g., "perky box" type) to protect them from mechanical damage and dust, and to limit radon emission. Store away from other minerals that may be sensitive to radiation. Display should be behind a barrier (e.g., in a display case) and away from areas of constant human presence.