Metazellerite
Chemical formula: Ca(U⁶⁺O₂)(CO₃)₂·3H₂O
Metazellerite is a rare, secondary uranium mineral, forming pale yellow to yellowish-green, fine crusts and coatings.
Properties
- Mohs hardness
- 2
- Color
- Pale yellow
- Luster
- Vitreous
- Streak
- Pale yellow
- Density
- 0
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The key diagnostic feature of metazellerite is its intense, greenish-yellow fluorescence under UV light. Identification is also based on its form of occurrence (fine acicular, felted aggregates), color, and co-occurrence with other secondary uranium minerals. Due to its radioactivity, it reacts to a Geiger counter. ## Distinguishing from Similar Minerals Metazellerite is visually almost identical to many other secondary uranium minerals of similar color and form, such as zellerite, andersonite, liebigite, or schröckingerite. Certain differentiation from zellerite is practically only possible using analytical methods, such as X-ray diffraction (XRD), due to differences in crystal structure and degree of hydration. It is often distinguished from other minerals in this group by its insolubility in water (unlike, for example, andersonite). ## Crystal Forms It forms very fine, elongated, acicular or platy crystals, which rarely occur individually. It typically forms dense, tangled clusters, rosette aggregates, and most commonly compact crusts and coatings.
Geological environment
## Genesis Metazellerite is a secondary mineral, formed in the oxidation (weathering) zones of uranium deposits. It forms as a result of carbonate-rich waters acting on primary uranium minerals, such as uraninite. It forms under low temperature and pressure conditions, often in voids and fractures of sedimentary rocks, such as sandstones. ## Mineral Associations It most often co-occurs with the mineral from which its name is derived – zellerite. It is also accompanied by other secondary uranium minerals, such as schröckingerite, gypsum, uranophane, as well as sulfides (pyrite, marcasite) and organic matter (charcoal). ## Localities The most important and classic localities for this mineral are in the USA, in Wyoming (Lucky Mc and other mines in Gas Hills, Fremont County). It has also been reported in small quantities in other uranium mining regions worldwide, but specimens from the type locality are the best known.
Rarity
Rare
For collectors
## Quality Criteria The collecting appeal of a metazellerite specimen depends on the intensity and saturation of the yellow color and the richness of the coating on the host rock. The most valued specimens are those on which, even under magnification, clearly formed, fine crystal aggregates are visible, and not just a uniform coating. Contrast with dark host rock also enhances aesthetic qualities. Due to the microscopic size of the crystals, their individual form or purity are not key criteria. ## Popular Localities By far the most sought-after and commonly found specimens in collections come from the classic locality in Gas Hills, Wyoming, USA. Material from this region is considered exemplary for this mineral.
Care and storage
## Cleaning Metazellerite specimens are generally not cleaned. Any attempts at mechanical or chemical cleaning will almost certainly destroy the delicate crystals. Only very careful removal of dust with a soft brush or a photographic air blower is permissible. ## What to Avoid Avoid contact with water, chemicals, as well as any vibrations and impacts. The crystals are extremely brittle. As a radioactive mineral, it requires special precautions – avoid inhaling dust and wash hands after each contact with the specimen. ## Storage Specimens should be stored in sealed, stable containers (e.g., "perky box" type), away from areas of frequent human presence, to minimize radiation exposure. It is necessary to clearly label the container as containing a radioactive mineral. Do not store it with radiation-sensitive minerals.