Metalodèvite

Chemical formula: Zn<sup>2+</sup>(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>·10H<sub>2</sub>O

A hydrated zinc uranyl arsenate of the autunite group, forming characteristic yellow, tabular crystals with strong fluorescence.

## Characteristics Metalodèvite is a secondary mineral of the autunite group, belonging to the arsenate class. It forms thin to thick, tabular crystals with a square outline, typical of this group. It most commonly occurs as rosette-like aggregates, micaceous lamellar aggregates, and as crusts. Its most characteristic visual feature is an intense yellow to greenish-yellow color. It is a highly radioactive mineral. ## Physical Properties Metalodèvite is relatively soft, with a Mohs hardness of 2-2.5. It has perfect, unidirectional cleavage parallel to the basal plane of the crystal {001}, which causes it to easily separate into thin lamellae. The luster is vitreous, becoming pearly on cleavage surfaces. It is transparent to translucent. It exhibits very strong, yellow-green fluorescence under ultraviolet light (both short-wave and long-wave). ## Colors and Varieties This mineral occurs in shades from lemon-yellow to greenish-yellow. No distinct color varieties or commercial varieties are recognized. ## History and Name The name metalodèvite refers to its type locality – the city of Lodève in France – and to its state of hydration. The prefix "meta-" indicates a lower degree of hydration compared to a hypothetical, fully hydrated counterpart (analogous to the meta-autunite and autunite pair). The mineral was described and approved as a new species in 1964. ## Uses Due to its rarity, radioactivity, and small accumulations, metalodèvite has no industrial applications. It is solely an object of interest for collectors and scientists.

Properties

Mohs hardness
2-2.5
Luster
Vitreous, Pearly
Streak
Light yellow
Density
3.65
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Tetragonal

Diagnostic features

## Identification Key diagnostic features of metalodèvite include its characteristic form of thin, tabular crystals, intense yellow color, perfect platy cleavage, and very strong yellow-green fluorescence under UV light. Radioactivity measurement using a Geiger counter is also an important indicator. ## Differentiation from Similar Minerals Metalodèvite is visually almost impossible to distinguish from other yellow minerals of the meta-autunite group, such as meta-autunite (does not contain zinc) or metakahlerite (contains iron instead of zinc). It can be confused with metazeunerite, which contains copper and usually has a greener hue. Certain identification requires advanced chemical analyses (e.g., EDS). ## Crystal Forms Crystals are tabular, with a square cross-section, developed parallel to the {001} plane. They usually form fan-shaped or rosette-like aggregates, as well as lamellar crusts and earthy masses.

Geological environment

## Genesis Metalodèvite is a secondary mineral, forming in the oxidation (weathering) zones of uranium deposits. Its crystallization requires the presence of zinc and arsenic ions in aqueous solutions, which originate from the weathering of associated minerals, such as sphalerite (a zinc mineral) and arsenopyrite or other arsenides (arsenic minerals). ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals, such as uranopilite, and with minerals from primary mineralization, such as uraninite, gypsum, pharmacolite, erythrite, and nickelskutterudite. ## Localities The most important and classic locality for this mineral is the Rabejac quarry near Lodève (Hérault, Occitanie) in France. Significant specimens also come from the Sophia mine in the Schapbach Valley in the Black Forest (Baden-Württemberg), Germany.

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, sharp crystals of intense, lemon-yellow color and good transparency are most valued by collectors. Rich aggregates of crystals in the form of rosettes or fans, embedded in a contrasting rock matrix, are also highly prized. Crystal size rarely exceeds a few millimeters, so larger specimens are sought after. ## Popular Localities Specimens from the type locality in Lodève, France, and from the Sophia mine in the German Black Forest are considered classic and most representative of this species.

Care and storage

## Cleaning Specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Contact with water is not recommended, as it can lead to changes in hydration and damage to the crystals. ## What to Avoid Metalodèvite is a brittle and soft mineral, susceptible to mechanical damage. As a hydrated mineral, it is sensitive to changes in temperature and humidity – storage in an overly dry environment (e.g., under strong lighting) can cause dehydration, leading to loss of transparency and cracking. It is highly radioactive and contains toxic arsenic – avoid inhaling dust and wash hands after any contact with the specimen. ## Storage It is recommended to store specimens in closed, airtight containers (e.g., "perky box" type) to stabilize humidity and limit radon emission. The container should be clearly labeled as radioactive material. It should be kept away from areas of permanent human habitation, especially bedrooms and living rooms.

Sources

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