Wölsendorfite

Chemical formula: Pb<sup>2+</sup><sub>7</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>14</sub>O<sub>19</sub>(OH)<sub>4</sub>·12H<sub>2</sub>O

Wölsendorfite is a rare uranium mineral, forming characteristic, tabular crystals of intense red color.

## Characteristics Wölsendorfite is a complex, hydrated lead and uranium oxide, occurring in the oxidation zones of uranium deposits. It forms very small, most often microscopic, tabular or bladed crystals. Its most characteristic feature is its intense red to orange-red color. It usually occurs as thin coatings, crusts, or rosette-like aggregates on host rocks. ## Physical Properties Wölsendorfite crystals are very brittle. The luster is most often vitreous to slightly resinous. It is a translucent mineral, and in very thin fragments, it can be transparent. Due to its uranium and lead content, it has a high density, approximately 6.8 g/cm³. ## Colors and Varieties This mineral is characterized by a consistent and distinctive palette of colors, from deep red, through reddish-orange, to orange. No color or commercial varieties are distinguished. ## History and Name The name Wölsendorfite comes from the location of its first discovery – fluorite veins in Wölsendorf, Bavaria (Germany). The mineral was described and named in 1957 by J. Protas. ## Uses Due to its rarity, small crystal size, and strong radioactivity, Wölsendorfite has no industrial application. It is of purely scientific importance and is sought after by specialized collectors of uranium minerals.

Properties

Mohs hardness
3.5
Luster
Vitreous
Streak
Orange-red
Density
6.8
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features of Wölsendorfite are its intensely red color, tabular crystal habit, and occurrence in the oxidation zones of uranium deposits. Strong radioactivity is also an important indicator. Under shortwave ultraviolet light, it exhibits weak, green fluorescence. ## Distinguishing from Similar Minerals It can be confused with other red secondary uranium minerals, such as Fourmarierite, which, however, has a different crystal habit and often forms larger aggregates. Final differentiation from similar uranyl oxides requires advanced research methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms thin, tabular crystals with a pseudohexagonal outline, often gathered in rosette-like or fan-shaped aggregates. It also occurs as fine-grained coatings and crusts.

Geological environment

## Genesis Wölsendorfite is a secondary uranium mineral, formed by the oxidation and weathering of primary uranium ores (mainly Uraninite) in the presence of lead-rich solutions. It forms under low temperature and pressure conditions, in the near-surface part of deposits. ## Mineral Associations It often co-occurs with other secondary uranium minerals, such as Fourmarierite, Uraninite, Kasolite, Soddyite, as well as with Fluorite, Quartz, and lead minerals, e.g., Galena. ## Localities The most important localities worldwide include the historical site in Wölsendorf (Bavaria, Germany), Shinkolobwe mine (Democratic Republic of Congo), La Creusaz mine (Switzerland), and deposits in the Great Bear Lake region (Canada).

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the intensity and uniformity of the red color are most important. Specimens with well-formed, sharp crystals forming aesthetic rosettes or fans on a contrasting matrix are highly valued. Crystal size is also crucial, as most specimens are microscopic – any crystal visible to the naked eye significantly increases its value. ## Popular Localities The most prized specimens, with the best-formed crystals, come from the Shinkolobwe mine in the Democratic Republic of Congo. Classic, though usually less spectacular, are also specimens from the type locality in Wölsendorf, Germany.

Care and storage

## Cleaning The mineral is extremely delicate and brittle. Mechanical or chemical cleaning is not recommended. Any dust can be removed very carefully with a soft brush or a photographic air blower. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. The crystals are sensitive to shocks and abrasions. As a secondary mineral, it is unstable under fluctuating humidity conditions. It is strongly radioactive – exposure should be limited, and inhalation of dust should be avoided. ## Storage Specimens should be stored in sealed, padded containers, preferably away from other minerals that could be damaged by radiation. Store in a dry place, away from heat sources and direct sunlight. Due to radioactivity, specimens should be kept out of reach of children and appropriately labeled.

Sources

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