Geschieberite

Chemical formula: K<sub>2</sub>(U<sup>6+</sup>O<sub>2</sub>)(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·2H<sub>2</sub>O

Geschieberite is a rare, secondary uranyl mineral, forming bright yellow, platy crystals and aggregates.

## Characteristics Geschieberite is a hydrated uranyl potassium sulfate. It occurs as very small, thin, platy crystals with a hexagonal outline, usually grouped into rosetted or spherical aggregates. Individual crystals rarely exceed 0.1 mm. Due to its chemical composition, this mineral exhibits strong radioactivity. ## Physical Properties Geschieberite crystals are brittle. Due to the small size of the crystals, most physical properties, such as hardness or density, have not been precisely measured, but only calculated. The mineral exhibits strong, green fluorescence under ultraviolet light (both short- and long-wave). ## Colors and Varieties Geschieberite has a characteristic bright yellow color. No color varieties or commercial varieties are known. ## History and Name The mineral's name comes from the German word "Geschiebe", meaning glacial erratic material. It refers to the fact that the mineral was first identified in a secondary deposit in glacial sediments. Geschieberite was described as a new mineral in 2014 by Jakub Plášil and his team. ## Applications Geschieberite has no industrial application. It is solely an object of scientific and collecting interest, sought after by specialists collecting uranium minerals.

Properties

Mohs hardness
~2
Luster
Pearly
Streak
Light yellow
Density
3.73
Cleavage
Perfect on {010}
Fracture
Micaceous
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features of geschieberite are its bright yellow color, occurrence as small, platy crystals forming rosetted aggregates, and strong green fluorescence under UV light. The most important feature, however, is its high radioactivity, easily detectable with a Geiger counter. ## Distinguishing from Similar Minerals Geschieberite can be confused with other secondary yellow uranium minerals, such as uranophane, carnotite, or zippeite. Distinguishing it from zippeite, with which it often co-occurs, is particularly difficult and usually requires advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy. The characteristic hexagonal outline of the crystals can be a helpful clue. ## Crystal Forms The mineral forms thin, platy crystals with a hexagonal habit, which combine into spherical or hemispherical aggregates and rosettes.

Geological environment

## Genesis Geschieberite is a secondary mineral, forming in the oxidation zone of uranium deposits. It forms as a result of weathering and alteration of primary uranium minerals, such as uraninite. It forms in sulfate-rich environments, often in voids and fractures in rocks. ## Mineral Associations This mineral often co-occurs with other secondary uranyl sulfates and silicates. It is most commonly associated with zippeite, uranophane, gypsum, and hydrated iron oxides (limonite/goethite). ## Localities The most important and type locality for geschieberite is the uranium mine dump in Königstein near Dresden in Saxony, Germany. This is the only confirmed locality from which well-formed specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of geschieberite depends on the richness and development of crystal aggregates on the rock matrix. Specimens with clearly visible, spherical or rosetted clusters of intense yellow color, contrasting with the darker host rock, are most valued. Due to the microscopic size of the crystals, quality assessment often requires magnification. ## Popular Localities The only source of collector specimens is the type locality - the Königstein mine dump in Germany. Specimens from this location are considered the best and only ones available on the market.

Care and storage

## Cleaning Geschieberite specimens should not be cleaned wet. Dust can only be removed with a soft brush or compressed air from a safe distance. Due to radioactivity, all handling should be done with caution, avoiding inhalation of dust. ## What to Avoid Contact with water and chemicals, which can dissolve or damage delicate crystals, should be strictly avoided. The mineral is sensitive to changes in humidity and temperature. It should not be heated or exposed to direct sunlight. ## Storage Geschieberite must be stored in a sealed, dry container, preferably away from other radiation-sensitive minerals. Due to its radioactivity, it should be kept out of reach of children and pets, and away from areas where people reside permanently. Appropriate labeling of the container with the ionizing radiation symbol is recommended.

Sources

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