Hügelite

Chemical formula: Pb²⁺₂(U⁶⁺O₂)₃(As⁵⁺O₄)₂O₂·5H₂O

Hügelite is a rare, radioactive uranyl lead arsenate, forming small, tabular crystals of orange-yellow to brown color.

## Characteristics Hügelite is a rare secondary mineral from the phosphuranylite group, belonging to the arsenate class. Chemically, it is a hydrated uranyl lead arsenate. It occurs as very small, tabular or bladed crystals, which often form rosetted or radial aggregates and crusts. Its crystals are usually too small to be observed with the naked eye. ## Physical Properties This mineral is characterized by low hardness, 2-3 on the Mohs scale, which makes it very brittle. It has a relatively high density, about 5.1 g/cm³, due to the presence of lead and uranium. Its luster is described as vitreous to greasy. It is transparent to translucent. ## Colors and Varieties Typical colors of hügelite range from orange-yellow, through yellowish-brown, to brown. No named varieties are distinguished. ## History and Name The mineral's name honors Baron Karl (or Carl) von Hügel (1795-1870), an Austrian diplomat, traveler, and naturalist. Hügelite was first described based on specimens from the Michael mine in Weiler (Baden-Württemberg, Germany). ## Uses Due to its rarity, small crystal size, and radioactivity, hügelite has no industrial applications. It is solely an object of interest for collectors specializing in uranium minerals and rare mineral species.

Properties

Mohs hardness
2-3
Luster
Vitreous to greasy
Streak
Light yellow
Density
5.1
Cleavage
Good on {100} Probable on {110}
Fracture
Conchoidal
Transparency
Transparent,Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of hügelite include its orange-yellow to brown color, occurrence as small, tabular crystals forming rosetted aggregates, and strong radioactivity. Identification most often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Hügelite can be confused with other secondary uranium minerals of similar color and habit, such as dewindtite, phosphuranylite, or dumontite. Certain differentiation is almost exclusively possible based on chemical analysis, which will show the simultaneous presence of lead, uranium, and arsenic. ## Crystal Forms Hügelite crystals are tabular or bladed, elongated and flattened. They usually occur as radial or rosetted aggregates, as well as thin crusts on the host rock.

Geological environment

## Genesis Hügelite is a secondary mineral, formed in the oxidation (weathering) zones of ore deposits containing uraninite and lead and arsenic minerals. It forms as a result of surface water action on primary minerals under oxygenated conditions. ## Mineral Associations This mineral co-occurs with other secondary uranium minerals. In its type locality (Michael mine in Germany), it was found in association with zeunerite, uranophane, kasolite, wulfenite, and mimetite, among others. ## Localities The most important and historical occurrence of hügelite is its type locality - the Michael mine in Weiler, Seelbach, in the German Black Forest. It is a very rare mineral, reported from only a few places worldwide.

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the intensity and attractiveness of the specimen's color, as well as the abundance and development of crystals, are most important. Specimens with clearly visible, well-formed crystal aggregates contrasting with the color of the host rock are most highly valued. Due to the microscopic size of the crystals, specimens are often evaluated under magnification. ## Popular Localities The only source of collector-quality hügelite specimens is its type locality in the Michael mine in Germany. Specimens from this location are considered classic and most desirable.

Care and storage

## Cleaning Hügelite specimens are extremely delicate and brittle. Mechanical cleaning is highly inadvisable. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust. Avoid contact with water and any chemicals. ## What to Avoid Hügelite is a radioactive mineral and should be handled with appropriate precautions. Avoid inhaling dust and direct skin contact. The mineral is very soft and susceptible to mechanical damage, shocks, and scratches. Protect it from moisture and chemicals. ## Storage Specimens should be stored in sealed, clearly labeled containers (e.g., "perky boxes"), away from other minerals that could be damaged by radiation. Store in a dry place, away from areas of constant human presence, to minimize radiation exposure.

External references

Sources

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