Metauranocircite II

Chemical formula: Ba(UO₂)₂(PO₄)₂·₆H₂O

Metauranocircite-II is a secondary mineral of the autunite group, distinguished by its intense yellow-green color and strong fluorescence under UV light.

## Characteristics Metauranocircite-II is a hydrated uranyl barium phosphate, belonging to the autunite group. It forms characteristic, tabular crystals with a square or octagonal outline, often aggregated into fan-shaped or rosette-like clusters. Specimens typically have an intense, yellow-green or lemon-yellow color. It is a highly radioactive mineral and exhibits bright green fluorescence under ultraviolet light (both shortwave and longwave). ## Physical Properties Metauranocircite-II crystals are soft and brittle, with a Mohs hardness of approximately 2.5. They have a vitreous luster, and a pearly luster on cleavage surfaces. They are transparent to translucent. The mineral's density is approximately 3.53 g/cm³. Due to its water content, it can easily undergo dehydration, leading to its destruction. ## Colors and Varieties This mineral occurs in shades from lemon-yellow to yellow-green. No distinct color varieties or commercial varieties are recognized. The name "metauranocircite" refers to its lower water content compared to uranocircite, from which it can form through partial dehydration. ## History and Name The name "uranocircite" comes from its uranium content and the location of its first discovery – "Circ" in Vogtland, Saxony (Germany). The prefix "meta-" was added to distinguish the form with a lower degree of hydration. The mineral was first described by Paul Gaubert in 1904 as a dehydration product of uranocircite. ## Uses Metauranocircite-II, like other uranium minerals, is of purely scientific and collector interest. Due to its radioactivity, it has no industrial applications, and its possession and transport may be subject to legal regulations.

Properties

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

Diagnostic features

## Identification Key diagnostic features of metauranocircite-II are its characteristic tabular crystal habit, intense yellow-green color, and very strong, bright green fluorescence under UV light. It is also a highly radioactive mineral, which can be easily confirmed with a Geiger counter. ## Distinguishing from Similar Minerals Metauranocircite-II is visually almost identical to other minerals of the autunite group, such as autunite, torbernite, metatorbernite, or uranocircite. It can only be distinguished from autunite (the calcium analogue) and torbernite (the copper analogue) by chemical analysis (EDS/XRF). It differs from uranocircite by a lower degree of hydration, which is impossible to determine visually. In collector practice, identification is most often based on a label from a reputable locality. ## Crystal Forms It forms thin, tabular crystals with a square or slightly elongated, rectangular outline. Crystals often arrange themselves into fan-shaped, rosette-like, or packet-like aggregates, and also form crusts and coatings on the host rock.

Geological environment

## Genesis Metauranocircite-II is a secondary mineral, forming in the oxidation (weathering) zones of uranium ore deposits. It forms as a result of the dehydration of uranocircite or direct crystallization from solutions rich in uranium, barium, and phosphates. Its presence is an indicator of the occurrence of primary uranium minerals, such as uraninite. ## Mineral Associations It most commonly co-occurs with other secondary uranium minerals, such as autunite, torbernite, uranophane, as well as with uraninite, quartz, fluorite, hematite, and manganese minerals (goethite, psilomelane). ## Localities Significant specimens come from Germany, especially from the Saxony region (Schlema-Hartenstein, Schneeberg) and the Bavarian Forest (Wölsendorf). It also occurs in the Czech Republic (Příbram), France (Rodès, Eastern Pyrenees), and in the USA, mainly in South Dakota (mines in Fall River County) and New Hampshire.

Rarity

Not very common

For collectors

## Quality Criteria The most prized specimens of metauranocircite-II are characterized by sharply defined, well-formed crystals with a large surface area, forming aesthetic, fan-shaped or rosette-like aggregates. The intensity and saturation of the yellow-green color also increase its value. Contrast with a dark host rock (matrix) and the absence of mechanical damage, which is very common for this brittle mineral, are important. ## Popular Localities Localities in Germany, especially Saxony, are considered classic and yield the best specimens. Specimens from Wölsendorf in Bavaria are also highly valued by collectors. Material from France and the USA is also found on the market.

Care and storage

## Cleaning Metauranocircite-II specimens are generally not cleaned. The crystals are extremely brittle, soft, and sensitive to water. Any contact with liquids or mechanical cleaning (even with a soft brush) risks irreversible damage to the delicate aggregates. Only very careful removal of loose contaminants using a photographic air blower is permissible. ## What to Avoid Absolutely avoid contact with water and other liquids, which can dissolve or damage the crystals. The mineral is sensitive to changes in humidity and temperature – heating leads to water loss and structural destruction. Avoid direct sunlight, which can cause fading. Due to radioactivity, avoid direct skin contact, inhalation of dust, and storage in areas of permanent human habitation. ## Storage Metauranocircite-II requires specialized conditions. It should be stored in a tightly sealed, transparent container (such as a "micromount" box or larger) to protect it from mechanical damage and humidity changes. The container should be clearly labeled as radioactive material. Store in a dry, cool place, away from other radiation-sensitive minerals and away from living areas.