Kroupaite
Chemical formula: KPb<sup>2+</sup><sub>0.5</sub>[(U<sup>6+</sup>O<sub>2</sub>)<sub>8</sub>O<sub>4</sub>(OH)<sub>10</sub>]·10H<sub>2</sub>O
Kroupaite is a very rare, secondary uranyl mineral, distinguished by its intense yellow color and occurrence as microscopic, acicular crystals.
Properties
- Luster
- Vitreous
- Streak
- Light yellow
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Kroupaite is identified by its characteristic crystal form – tiny, acicular or platy crystals forming radial aggregates. The intense yellow color and strong radioactivity are key features. Final identification requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other secondary uranyl minerals of similar color and form, such as becquerelite, schoepite, or studtite. Distinguishing it with the naked eye is practically impossible. Kroupaite is distinguished by its unique chemical composition (presence of potassium and lead) and specific crystallographic parameters, which allow for its identification under laboratory conditions. ## Crystal Forms It forms very fine, acicular crystals, elongated along the [010] axis, often flattened. These crystals combine into radial, stellate, or tangled aggregates, and also form crusts on the host rock.
Geological environment
## Genesis Kroupaite is a secondary mineral, formed as a result of weathering and oxidation processes of primary uranium ores (mainly uraninite) in the presence of potassium- and lead-rich solutions. It forms under low-temperature conditions within the oxidation zone of hydrothermal deposits. ## Mineral Associations It occurs in association with other secondary uranium minerals. In the type locality (Jáchymov), its co-occurrence with becquerelite, schoepite, fourmarierite, curite, kasolite, anglesite, and also with uraninite as a primary mineral, has been observed. ## Localities The only confirmed and described occurrence of kroupaite in the world is its type locality – the Svornost Mine in Jáchymov, Karlovy Vary Region, Czech Republic.
Rarity
Extremely rare
For collectors
## Quality Criteria The collector's appeal of a specimen depends on the richness and development of the crystal aggregates. Samples with distinct, radial clusters of acicular crystals, contrasting well with the host rock, are most valued. The crystal size is microscopic, so the aesthetics of the entire aggregate are primarily assessed. ## Popular Localities The only source of kroupaite specimens is the Svornost Mine in Jáchymov (Czech Republic). Material from this locality is extremely rare and sought after by specialized collectors of uranium minerals.
Care and storage
## Cleaning Kroupaite specimens are generally not cleaned due to their extreme delicacy and radioactivity. Any attempt at mechanical cleaning (e.g., with a brush) will inevitably destroy the microscopic crystals. Dust can only be removed using a photographic air blower or compressed air from a distance. ## What to Avoid Contact with water and chemicals should be strictly avoided. The mineral is sensitive to changes in humidity and temperature. As a uranyl mineral, it may be sensitive to prolonged exposure to sunlight. Due to radioactivity, direct skin contact, inhalation of dust, and storage in areas of permanent human presence should be avoided. ## Storage Specimens should be stored in sealed, lead-lined or thick acrylic containers (so-called perky boxes) that limit radiation emission. The container should be clearly marked with the international radioactivity symbol. Store in a dry place, away from heat and light sources.