Paulscherrerite

Chemical formula: U⁶⁺O₂(OH)₂

Paulscherrerite is a very rare, secondary uranium mineral with an intense, canary-yellow color, occurring in the oxidation zones of uranium deposits.

## Characteristics Paulscherrerite is a hydrated uranyl oxide belonging to the schoepite group. It forms microscopic, platy or bladed crystals, which typically occur as earthy, powdery, or compact aggregates and coatings. Its most distinctive feature is its intense, canary-yellow color. Due to its chemical composition, this mineral is strongly radioactive. ## Physical Properties The crystals are extremely small, which makes precise determination of physical properties difficult. The mineral exhibits strong, greenish-yellow fluorescence under ultraviolet light (both longwave and shortwave). The density calculated from the formula and cell parameters is 6.66 g/cm³. ## Colors and Varieties Paulscherrerite occurs exclusively in canary-yellow. No color varieties or commercial varieties are distinguished. ## History and Name The mineral was described in 2007 by Joël Brugger, Sergey Krivovichev, Nicolas Meisser, Stefan Ansermet, Thomas Armbruster, and Peter C. Burns. Its name honors Paul Scherrer (1890-1969), a Swiss physicist who made significant contributions to the development of X-ray crystallography, co-developing the Debye–Scherrer powder method. Approval by the International Mineralogical Association (IMA) occurred in 2006 (IMA2006-032). ## Applications Paulscherrerite, due to its extreme rarity and microscopic size, has no industrial application. It is solely an object of scientific and collecting interest for specialized collectors of uranium minerals.

Properties

Luster: Earthy
Streak: canary yellow
Density: 6.66
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Paulscherrerite is identified by its intense, canary-yellow color, earthy or powdery habit, and strong radioactivity. A key diagnostic feature is its strong, greenish-yellow fluorescence under UV light. However, definitive identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with many other yellow secondary uranium minerals, such as carnotite, tyuyamunite, uranophane, or schoepite. Distinguishing it from schoepite, to which it is structurally related, is impossible without laboratory analysis. Many of these minerals have a similar appearance and also exhibit fluorescence, so visual identification is at best indicative. ## Crystal Forms It forms microscopic, platy crystals with dimensions not exceeding a few micrometers. It occurs mainly as very fine-grained, earthy or powdery coatings and masses.

Geological environment

## Genesis Paulscherrerite is a secondary uranium mineral, formed in the oxidation (weathering) zones of uraninite deposits. It forms as a result of dehydration of metaschoepite under conditions of low relative humidity. It is a product of the alteration of other, more hydrated uranyl oxides. ## Mineral Associations This mineral co-occurs with other secondary uranium minerals. At the type locality (Mount Painter, Australia), it was found in association with ianthinite, uraninite, metaschoepite, fourmarierite, wölsendorfite, and boltwoodite. It also occurs with quartz and hematite. ## Localities Paulscherrerite is an extremely rare mineral. Besides the type locality at Mount Painter No. 2 in South Australia, its occurrence has only been confirmed in a few places worldwide, including the Shinkolobwe mine in the Democratic Republic of Congo and the Ruggles mine in Grafton, New Hampshire, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to the microscopic nature of the crystals, the main criterion for evaluation is the richness and surface area of the coating on the host rock. Specimens with intensely colored, thick, and extensive aggregates of paulscherrerite are most valued. Contrast with a dark host rock (matrix) also enhances visual appeal. The presence of well-defined (though still microscopic) crystals would be an exceptional feature, but this is extremely rare. ## Popular Localities The only source of specimens of collecting significance is the type locality – Mount Painter in Australia. Specimens from other confirmed localities are usually purely scientific material and practically unavailable on the market.

Care and storage

## Cleaning Paulscherrerite specimens should generally not be cleaned. Any attempts at mechanical or chemical cleaning can permanently damage the delicate, microscopic crystals or entire aggregates. If absolutely necessary, dust can be carefully removed with a photographic air blower. ## What to Avoid Contact with water and chemicals must be strictly avoided. As a secondary mineral, it is sensitive to changes in humidity and can undergo dehydration or recrystallization. It should be protected from high temperatures, direct sunlight, and vibrations. Due to its strong radioactivity, exposure should be limited, and hands should always be washed after handling the specimen. ## Storage Specimens should be stored in airtight, lead-lined or thick plastic containers, away from other minerals that could be damaged by radiation. The container should be clearly marked with a radioactivity symbol. Store in a dry, temperature-stable place, inaccessible to children and pets.