Metavanuralite
Chemical formula: Al(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(V<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)·8H<sub>2</sub>O
Metavanuralite is a rare, highly radioactive secondary mineral of the uranyl vanadate group, forming characteristic lemon-yellow coatings and aggregates.
Description
## Characteristics Metavanuralite is a hydrated uranyl aluminum vanadate, belonging to the secondary minerals. It occurs in the oxidation zones of uranium-vanadium deposits. It most often forms earthy or powdery coatings, as well as fine-grained aggregates and clusters of small, bladed crystals. Its most characteristic feature is its intense, lemon-yellow or canary-yellow color. It is a highly radioactive mineral. ## Physical Properties Metavanuralite is very soft, with a Mohs hardness of about 2. It is brittle, and its density is about 3.63 g/cm³. It exhibits perfect cleavage in one direction, which gives its aggregates a pearly luster on cleavage surfaces. Apart from these surfaces, the luster is dull or earthy. It is translucent and does not show fluorescence under ultraviolet light. ## Colors and Varieties This mineral occurs in uniform, light yellow shades, from lemon-yellow to canary-yellow. No color or commercial varieties are distinguished. ## History and Name Metavanuralite was first described in 1970 by Fabien Cesbron. Its name refers to its chemical composition (vanadium, uranium, aluminum) and to the fact that it is a less hydrated form of vanuralite (the prefix "meta-" indicates a lower water content). The type locality is the Mounana mine in Gabon. ## Uses Due to its rarity and small size of aggregates, metavanuralite has no industrial application. It is solely an object of scientific interest and a valued collector's mineral.
Diagnostic features
## Identification The key features allowing identification of metavanuralite are its intensely lemon-yellow color, occurrence as coatings and microcrystalline aggregates on sandstones, and very strong radioactivity, easily detectable with a Geiger counter. The pearly luster on cleavage surfaces is also a helpful feature. ## Distinguishing from Similar Minerals Metavanuralite can be confused with other yellow secondary uranium minerals, such as carnotite, tyuyamunite, or francevillite. Carnotite is usually more dull and powdery. Tyuyamunite often exhibits greenish hues and fluoresces under UV light, unlike metavanuralite. Final distinction of these minerals often requires advanced studies, e.g., X-ray diffraction (XRD). ## Crystal Forms Metavanuralite forms aggregates of very small, platy or bladed crystals, which often arrange into rosette-like forms. Less commonly, it occurs as radial aggregates or simply as earthy coatings on the host rock.
Geological environment
## Genesis Metavanuralite is a secondary mineral, formed as a result of weathering and oxidation of primary uranium and vanadium ores (such as uraninite) in sedimentary deposits, mainly sandstones. It crystallizes from aqueous solutions under near-surface conditions. ## Mineral Associations It most often co-occurs with other secondary uranium and vanadium minerals, such as vanuralite (of which it is a dehydration product), francevillite, curienite, as well as carnotite and tyuyamunite. Gypsum can also be an associated mineral. ## Localities The most important and classic locality for metavanuralite, from which the best specimens originate, is the Mounana uranium mine near Franceville in Gabon. It is also known from some deposits in the San Rafael Swell area in Utah, USA.
Rarity
Rare
Collector aspects
## Quality Criteria The most highly valued by collectors are specimens with rich, intensely colored coatings on a contrasting sandstone matrix. Samples with visible, even under magnification, microcrystals forming rosette-like aggregates are also highly rated. The value of a specimen is enhanced by the presence of other rare secondary minerals from the same association. ## Popular Localities Specimens from the type locality – the Mounana mine in Gabon – are by far the most sought after and highly valued on the collector's market. Material from this locality is considered the global standard for this mineral.
Care and storage
## Cleaning Metavanuralite specimens should only be cleaned dry, using a soft brush or a gentle stream of compressed air to remove dust. Contact with water and any chemical agents must be strictly avoided, as they can damage or chemically alter this delicate mineral. ## What to Avoid Metavanuralite is highly radioactive. Direct, prolonged skin contact should be avoided, and hands should be thoroughly washed after each contact with a specimen. Inhalation of dust or ingestion of its particles must not be allowed. The mineral is very soft, brittle, and sensitive to changes in humidity, so it should be protected from mechanical damage, shocks, and sudden changes in environmental conditions. ## Storage Due to its radioactivity, specimens should be stored in tightly sealed, lead or glass containers, away from areas of permanent human presence (especially bedrooms and living rooms). The container must be clearly marked with a radioactivity symbol. It should not be stored in direct proximity to other minerals that may be sensitive to radiation (e.g., causing darkening of smoky quartz).