Uranotungstite
Chemical formula: Ba(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>W<sup>6+</sup><sub>2</sub>O<sub>8</sub>(OH)<sub>2</sub>·H<sub>2</sub>O
Uranotungstite is a very rare, radioactive secondary mineral, a hydrated uranyl and barium tungstate, found in the oxidation zones of tungsten deposits.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous to Pearly
- Streak
- Light yellow
- Density
- 6.35
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Key diagnostic features of uranotungstite include its characteristic canary-yellow color, specific crystal forms (thin blades forming rosette-like or stellar aggregates), and strong radioactivity. This mineral also exhibits intense, greenish-yellow fluorescence under ultraviolet light (both shortwave and longwave). ## Distinguishing from Similar Minerals Uranotungstite can be confused with other yellow secondary uranium minerals, such as uranophane, boltwoodite, or cuprosklodowskite. Distinguishing it requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS), due to visual similarities and co-occurrence. The characteristic stellar aggregates can be a helpful visual clue. ## Crystal Forms Uranotungstite crystallizes as very small, thin, bladed crystals, elongated along the [100] axis and flattened parallel to {010}. These crystals often combine to form stellar or rosette-like aggregates, as well as radial and spherulitic masses and thin crusts on the host rock.
Geological environment
## Genesis Uranotungstite is a secondary mineral that forms in the oxidation zones of hydrothermal deposits containing tungsten minerals (mainly wolframite and scheelite) and uranium (uraninite). It forms as a result of surface waters acting on these primary minerals under conditions of low temperatures and pressures. ## Mineral Associations This mineral co-occurs with other secondary uranium and tungsten minerals. In its type locality (Clara mine), it was found in association with uraninite, wolframite, scheelite, hematite, quartz, barite, fluorite, and other rare secondary minerals such as stolzite, tungstite, cuprosklodowskite, uranophane, and kasolite. ## Localities Uranotungstite is an extremely rare mineral. Besides its type locality – the Clara mine in the Black Forest, Germany – its occurrence has been confirmed in only a few other places worldwide, including the La Muela mine in Ponferrada (Spain) and the Carrizal area in Chile.
Rarity
Extremely rare
For collectors
## Quality Criteria Due to its extreme rarity, every confirmed specimen of uranotungstite is valuable for specialized collections. Micromounts showing well-formed, stellar or rosette-like crystal aggregates of intense, canary-yellow color are most highly prized. The aesthetic composition with associated minerals on a small fragment of host rock is also important. ## Popular Localities The vast majority of the best and most well-known uranotungstite specimens come from its type locality – the Clara mine in the Rankach Valley, Black Forest (Germany). This is a classic locality for many rare secondary minerals.
Care and storage
## Cleaning Due to its extreme rarity, small size, and fragility of crystals, mechanical cleaning is inadvisable and practically impossible. Specimens should be protected from dust. ## What to Avoid Uranotungstite is a stable mineral, but contact with chemicals and ultrasonic cleaners should be avoided. As a radioactive mineral, it requires safe handling and storage away from other minerals that could be damaged by radiation. Inhaling dust and direct skin contact should be avoided. ## Storage Uranotungstite specimens should be stored in specialized, lead-lined containers or in a way that minimizes radiation exposure. They should be kept in a dry place, away from sunlight, and in a well-ventilated room. Containers should always be clearly labeled as containing radioactive material.