Metatyuyamunite
Chemical formula: Ca(U⁶⁺O₂)₂(V⁵⁺O₄)₂·3H₂O
Metatyuyamunite is a uranium and vanadium mineral from the carnotite group, forming bright yellow, earthy coatings and aggregates, and is a dehydration product of tyuyamunite.
Properties
- Mohs hardness
- 2
- Luster
- Pearly, Waxy, Dull
- Streak
- Yellow
- Density
- 3.81
- Cleavage
- {001}
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Metatyuyamunite is most easily recognized by its intense, bright yellow color, low hardness, and occurrence as earthy coatings or small, scaly crystals. A key diagnostic feature is strong, yellowish-green fluorescence under UV light. It is also highly radioactive, which can be easily detected with a Geiger counter. ## Distinguishing from Similar Minerals Metatyuyamunite is visually almost identical to tyuyamunite. The difference lies in the degree of hydration, which is impossible to verify with amateur methods. In collecting practice, many specimens are mislabeled. Differentiation requires X-ray diffraction (XRD) analysis. It can be confused with other secondary uranium minerals, such as carnotite (contains potassium instead of calcium, often has a more greenish hue) or autunite (intensely fluorescent, but crystallizes in the tetragonal system, forming characteristic square tablets). Identification without specialized equipment is very difficult. ## Crystal Forms Crystals are rare, most often appearing as very small, thin tablets with a rhombic outline. It usually forms microcrystalline, earthy, dusty, or powdery coatings and crusts. Scaly, rosette-like, and fan-shaped aggregates are also found.
Geological environment
## Genesis Metatyuyamunite is a secondary mineral, forming exclusively in the oxidation zone of uranium and vanadium deposits. It forms as a result of dehydration of tyuyamunite under conditions of low humidity and temperature. This process is reversible – in the presence of water, metatyuyamunite can transform back into tyuyamunite. It most often occurs in porous sandstones, where it precipitates from groundwater saturated with uranium, vanadium, and calcium. ## Mineral Associations This mineral co-occurs with other secondary uranium and vanadium minerals. Its most common associate is tyuyamunite, from which it forms. Other associated minerals include carnotite, uranophane, gypsum, calcite, and iron and manganese oxides. ## Localities The most important and classic localities for metatyuyamunite are on the Colorado Plateau in the USA, particularly in New Mexico (Shiprock and Grants districts, including the Haystack mine), Arizona (Lukachukai Mountains), and Utah. It is also known from many other uranium deposits worldwide where tyuyamunite occurred.
Rarity
Not very common
For collectors
## Quality Criteria Specimens with well-formed, even microscopic, crystals forming fan-shaped or rosette-like aggregates on a contrasting rock matrix are most valued by collectors. An intense, pure, canary-yellow color is also highly prized. Due to the prevalence of earthy forms, even a rich coating of vibrant color on an aesthetic rock can be an attractive specimen. Precise locality information is important, especially if it comes from classic sites in the USA. ## Popular Localities The most known and valued localities from which metatyuyamunite specimens originate include historical uranium mines on the Colorado Plateau in the USA. Specimens from mines in the Grants and Shiprock areas of New Mexico and from the Lukachukai Mountains in Arizona are considered classic.
Care and storage
## Cleaning Metatyuyamunite specimens should not be cleaned with water. Water can cause rehydration of the mineral and its gradual transformation back into tyuyamunite, as well as damage delicate, brittle aggregates. To remove dust, use only a soft brush or compressed air from a safe distance. ## What to Avoid Contact with water and other liquids must be strictly avoided. The mineral is sensitive to changes in humidity. It should not be heated, as this leads to further water loss and possible structural change. As a highly radioactive mineral, it requires careful handling – avoid inhaling dust and wash hands after each contact. ## Storage Metatyuyamunite specimens should be stored in dry conditions, preferably in sealed, airtight containers (e.g., "perky box" type), which protect them from moisture and mechanical damage. Due to radioactivity, they should be kept away from areas of permanent human habitation and other minerals that could be damaged by radiation.