Braunerite
Chemical formula: K<sub>2</sub>Ca(U<sup>6+</sup>O<sub>2</sub>)(CO<sub>3</sub>)<sub>3</sub>·6H<sub>2</sub>O
Braunerite is an extremely rare, radioactive uranyl mineral, forming microscopic, yellow crystals and coatings.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous to Pearly
- Streak
- Light yellow
- Density
- 2.95
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Key diagnostic features include its pale yellow color, the form of small, acicular or platy crystals forming radial aggregates, and very strong, green fluorescence under UV light. Occurrence in paragenesis with other secondary uranium minerals in known localities is also an important clue. ## Distinguishing from Similar Minerals Braunerite can be confused with many other secondary, yellow uranium minerals, such as liebigite, andersonite, schröckingerite, or bayleyite. Liebigite and andersonite crystallize in different systems and often form granular coatings. Schröckingerite and bayleyite also have a similar appearance and fluorescence. Definitive differentiation is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy. ## Crystal Forms Crystals are elongated, platy or acicular, with a rhombic cross-section. They usually occur as radial or spherulitic aggregates and rosettes, as well as thin coatings and crusts on the host rock.
Geological environment
## Genesis Braunerite is a secondary mineral, forming in the oxidation zones of uraninite deposits. It forms as a result of the action of carbonate-rich waters on primary uranium ores. It is a typical post-mining mineral, crystallizing on the walls of old mine workings and on dumps, under conditions of low temperature and pressure. ## Mineral Associations This mineral co-occurs with other secondary uranium minerals, such as schröckingerite, liebigite, andersonite, bayleyite, swartzite, as well as with gypsum, aragonite, and uraninite as the primary mineral. ## Localities The only confirmed and described locality (type locality) for this mineral is the dumps of the Svornost mine in Jáchymov, in the Karlovy Vary region of the Czech Republic.
Rarity
Extremely rare
For collectors
## Quality Criteria As an extremely rare "micromineral," every authentic braunerite specimen is valuable to specialized collectors. Samples with rich, well-formed, radial crystal aggregates, clearly visible under a microscope, are most highly prized. The aesthetics of the specimen are also important – the contrast of the yellow crystals with the host rock and the presence of associated minerals. ## Popular Localities The only source of specimens is the type locality – the Svornost mine in Jáchymov, Czech Republic. Collecting material comes from old mine dumps.
Care and storage
## Cleaning The mineral is extremely delicate and soluble in water and acids. It should absolutely not be cleaned wet. Any contaminants can only be removed mechanically, with the utmost care, using, for example, a soft brush or compressed air from a safe distance. ## What to Avoid Avoid contact with water, water vapor, moisture, and any chemicals that could damage or dissolve it. As a strongly radioactive mineral, it requires specialized handling and storage with adherence to radiological protection principles. Direct, prolonged contact and inhalation of dust should be avoided. ## Storage Specimens should be stored in sealed, dry containers (e.g., "perky box" type), away from other radiation-sensitive minerals. The container must be clearly labeled as radioactive material. Store in a place inaccessible to children and pets.