Arsenuranylite

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

Arsenuranylite is a rare, highly radioactive secondary uranium mineral, forming characteristic yellow to orange-yellow coatings and crusts.

## Characteristics Arsenuranylite is a hydrated calcium uranyl arsenate. It most commonly occurs as earthy or powdery coatings, as well as thin crusts and films on other uranium minerals. Rarely, it forms microscopic tabular or bladed crystals, which may be aggregated into rosette-like or radial forms. Due to its characteristic, bright color, it is easily noticeable in the oxidation zones of uranium deposits. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2. It has a density ranging from 3.66-3.88 g/cm³. The luster is typically dull or earthy for aggregates, and vitreous to waxy on rare crystal surfaces. It is a highly radioactive mineral. ## Colors and Varieties Arsenuranylite exhibits colors from yellow, through golden-yellow, to orange-yellow. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1958 by Jacques-Fabien de Lapparent, directly refers to its chemical composition – it contains an arsenate group (arsen-) and a uranyl group (-uranyl-). It was discovered and described based on samples from the uranium mine in Lachaux, France. ## Uses Arsenuranylite has no industrial application. It is of purely scientific and collector's interest as a rare secondary uranium mineral.

Properties

Mohs hardness
2
Luster
Dull, Earthy, Vitreous
Streak
Light yellow
Density
3.66-3.88
Cleavage
None
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features include its bright, yellow-orange color, occurrence as earthy coatings and crusts in the oxidation zones of uranium deposits, and very strong radioactivity. Under shortwave ultraviolet light, it exhibits weak, green fluorescence. ## Distinguishing from Similar Minerals Arsenuranylite can be confused with other secondary uranium minerals of similar color, such as uranophane, autunite, or torbernite. Differentiation often requires chemical analysis (test for arsenic) or X-ray diffraction (XRD) studies. Compared to the often vitreous and better-formed crystals of autunite, arsenuranylite primarily forms earthy and dull aggregates. ## Crystal Forms Crystals are extremely rare and appear as microscopic, thin, hexagonal tablets or blades. It typically forms earthy, powdery, rosette-like, or radial aggregates, as well as thin crusts.

Geological environment

## Genesis Arsenuranylite is a secondary mineral, forming in the oxidation (weathering) zones of arsenic-rich uranium deposits. It forms as a result of the alteration of primary uranium minerals, such as uraninite, in the presence of arsenic-containing solutions. ## Mineral Associations It often co-occurs with other secondary uranium minerals, such as uranophane, phosphuranylite, torbernite, zeunerite, as well as with uraninite (as a primary mineral), quartz, and hematite. ## Localities Important localities worldwide include Lachaux (Puy-de-Dôme) in France (type locality); Rabejac mine in Hérault, France; Menzenschwand and Wittichen in the Black Forest, Germany; Jáchymov in the Czech Republic; and some deposits in Utah, USA.

Rarity

Rare

For collectors

## Quality Criteria Specimens with visible, even microscopic, crystals forming rosette-like or radial aggregates are most valued by collectors. Intense, bright color and contrast with the host rock are important. Due to its rarity, even rich coatings and crusts on rock matrix are considered valuable. ## Popular Localities Specimens from classic European localities, such as Menzenschwand in Germany or Rabejac in France, are particularly sought after by specialists collecting uranium minerals.

Care and storage

## Cleaning Arsenuranylite specimens should generally not be wet-cleaned. Dust and loose particles can be removed very carefully using a soft brush or a photographic air blower. Due to its fragility and softness, any mechanical contact should be avoided. ## What to Avoid Contact with water and chemicals must be strictly avoided. The mineral is sensitive to humidity changes. As a highly radioactive mineral, it requires special precautions – avoid inhaling dust and direct skin contact. Hands should be thoroughly washed after any contact. ## Storage Arsenuranylite specimens must be stored in sealed, clearly labeled containers with a radioactivity warning label. They should be kept away from other minerals that could be damaged by radiation. Store in a dry place, away from heat sources and areas of permanent human presence.

Sources

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