Uranocircite I

Chemical formula: Ba(UO₂)₂(PO₄)₂·12H₂O

Uranocircite I is a hydrated uranyl barium phosphate, a mineral from the autunite group, characterized by an intense yellow-green color and strong fluorescence.

## Characteristics Uranocircite I is a mineral belonging to the autunite group, being a hydrated uranyl barium phosphate. It forms characteristic, thin, tabular crystals with a square or rectangular outline, often with truncated corners. These crystals usually occur in rosette-like or fan-shaped aggregates, as well as in earthy, powdery aggregates, or as coatings and crusts on the host rock. Its intense, lemon-yellow to greenish-yellow color is very characteristic. ## Physical Properties Uranocircite I is a relatively soft mineral, with a Mohs hardness of 2-2.5. The crystals are brittle, and their surfaces often exhibit a pearly luster, especially on cleavage planes. In other areas, the luster is vitreous or dull in the case of earthy aggregates. It is transparent to translucent. This mineral is strongly radioactive. ## Colors and Varieties This mineral occurs in shades from lemon-yellow to greenish-yellow. No distinct color varieties or commercial varieties are distinguished. The name "Uranocircite I" refers to its specific hydration state (12 water molecules); there is also Uranocircite II (or Metauranocircite) with a lower water content. ## History and Name The mineral's name refers to its chemical composition – the presence of uranium – and to the location of its first discovery in Saxony, Germany, near the town of Falkenstein, whose coat of arms depicts a falcon (Greek "kirkos"). It was first described in 1877 by Albinus Weiskopf. ## Uses Due to its rarity and strong radioactivity, Uranocircite I has no industrial applications. It is solely an object of interest for mineral collectors and scientific institutions. Due to its radioactivity, its collection and storage require specialized knowledge and precautions.

Properties

Mohs hardness
2-2.5
Luster
Vitreous, Pearly
Streak
Pale yellow
Density
3.53
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Tetragonal

Diagnostic features

## Identification The most important diagnostic features of Uranocircite I are its intense, lemon-yellow to greenish-yellow color, thin-tabular crystal habit, and very strong, bright green fluorescence under ultraviolet light (both shortwave and longwave). Strong radioactivity, easily detectable with a Geiger counter, is a key identifying feature. ## Distinguishing from Similar Minerals Uranocircite I can be confused with other uranyl minerals from the autunite group, such as Autunite (with calcium instead of barium) or Torbernite (green, with copper). Distinguishing it from Autunite often requires chemical analysis to confirm the presence of barium. It differs from other yellow secondary minerals (e.g., Carnotite) by its crystal form and fluorescence intensity. ## Crystal Forms Crystals are thin-tabular, with a square or rectangular outline, forming fan-shaped, rosette-like, or layered aggregates. It often forms crusts and coatings on rock surfaces.

Geological environment

## Genesis Uranocircite I is a secondary mineral, forming in the oxidation zones of uranium ore deposits. It originates from the weathering and alteration of primary uranium minerals, such as uraninite. It requires the presence of phosphate ions and barium in circulating solutions within the rock. ## Mineral Associations It often co-occurs with other secondary uranium minerals, such as Autunite, Torbernite, Uraninite (as a primary mineral), as well as associated minerals like quartz, feldspars, hematite, and goethite. ## Localities The most important and classic localities, from which good quality specimens originate, are Germany (Saxony, including Bergen, Streuberg mine; Bavaria), France (Lachaux in Auvergne), and Brazil (Minas Gerais). It also occurs in other uranium deposits worldwide, including the USA (South Dakota) and Australia.

Rarity

Rare

For collectors

## Quality Criteria The most valued Uranocircite I specimens by collectors are characterized by well-formed, sharp crystals with an intense, lemon-yellow color. Large, undamaged fans or rosettes of crystals on a contrasting, dark rock matrix achieve the highest value. The aesthetic composition and minimal damage to delicate crystals are also important. ## Popular Localities Specimens from historical localities in Saxony (Germany) are considered classics and are highly sought after. High-quality crystals also come from Lachaux in France and from some pegmatites in Brazil.

Care and storage

## Cleaning Cleaning Uranocircite I specimens is generally not recommended due to their fragility and radioactivity. If absolutely necessary, a very soft, dry brush can be used to remove dust. Avoid contact with water, which can alter the mineral's hydration state and lead to its degradation. ## What to Avoid - **Water and moisture:** Contact with water or storage in a humid environment can lead to alteration to Metauranocircite or crystal disintegration. - **High temperature and dry air:** These cause dehydration, i.e., loss of water from the crystal lattice, which destroys the mineral's structure. - **Sunlight:** Prolonged exposure can cause color fading. - **Vibrations and impacts:** Crystals are extremely brittle and easily susceptible to mechanical damage. - **Direct skin contact:** Due to high radioactivity, direct contact must be strictly avoided. Always use protective gloves. ## Storage Uranocircite I specimens must be stored with the utmost caution. They should be kept in sealed, lead or thick glass containers to minimize radiation. Containers should be clearly labeled as radioactive material. Store in a dry, cool, and dark place, away from people and animals, and also away from other minerals that could be damaged by radiation.

External references

Sources

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