Metauroxite
Chemical formula: (U⁶⁺O₂)₂((C₂)⁶⁺O₄)(OH)₂(H₂O)₂
Meta-autunite is a very rare, secondary uranyl mineral, occurring as yellow, microscopic crystals and coatings.
Properties
- Mohs hardness
- 2
- Color
- Light yellow
- Luster
- Vitreous
- Streak
- Very pale yellow
- Density
- 4.403
- Cleavage
- Two good cleavages probably on {101} and {010} based on the structure.
- Fracture
- Irregular/Uneven
- Transparency
- Transparent
- Crystal system
- Triclinic
Diagnostic features
## Identification Identification of meta-autunite is primarily based on its characteristic, bright yellow color, mode of occurrence (fine needles, coatings), and geological environment (oxidation zones of uranium deposits). A key diagnostic feature is strong, yellowish-green fluorescence under shortwave ultraviolet (UV-SW) light. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other yellow secondary uranium minerals, such as uranophane, autunite, or tyuyamunite. Distinguishing it with the naked eye is practically impossible. Meta-autunite is distinguished by its unique chemical composition (it is an oxalate), which can only be confirmed in the laboratory. ## Crystal Forms It forms elongated, platy or acicular crystals, often grouped into radial aggregates (spherulites) or forming thin crusts and coatings.
Geological environment
## Genesis Meta-autunite is a secondary mineral, formed in the oxidation zones of uranium deposits. Its genesis is likely associated with the interaction of solutions rich in oxalic acid (of organic origin, e.g., from the decomposition of lichens or other organic matter) with earlier uranium minerals. ## Mineral Associations It co-occurs with other uranium minerals, such as uraninite (of which it is an oxidation product), as well as with other rare uranyl oxalates, such as uranoxite and moolooite. ## Localities The only confirmed and described occurrence of this mineral (type locality) is the Schlema-Alberoda uranium deposit in the Ore Mountains (Erzgebirge) in Saxony, Germany.
Rarity
Extremely rare
For collectors
## Quality Criteria As an extremely rare "micromineral," every analytically confirmed specimen is valuable to specialized collectors. Highly prized are specimens with visible, even under a microscope, well-formed crystals or rich, brightly colored coatings on a small rock matrix. Accurate locality documentation is crucial. ## Popular Localities The only source of specimens is the historical type locality in Schlema-Alberoda, Germany. Specimens are practically unavailable on the commercial market and are mainly found in institutional and systematic collections.
Care and storage
## Cleaning Due to its extreme rarity, fragility, and microscopic crystal size, mechanical cleaning is inadvisable. Specimens should be protected from dust by storing them in sealed containers. ## What to Avoid Meta-autunite is a uranium mineral and is radioactive – it should be handled with appropriate precautions (avoiding dust inhalation, washing hands after contact). Avoid contact with water and chemicals. It is sensitive to heat. ## Storage Specimens should be stored in specialized, sealed containers for radioactive minerals, away from other minerals that could be damaged by radiation. Store in a dry place, away from direct sunlight and heat sources.