Běhounekite
Chemical formula: U<sup>4+</sup>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·4H<sub>2</sub>O
Běhounekite is a very rare, radioactive uranium sulfate, forming characteristic green platy crystals in the oxidation zones of uranium deposits.
Description
## Characteristics Běhounekite is a secondary uranium mineral, occurring as small but well-formed crystals. It typically forms thin, platy crystals with a hexagonal outline, which can combine into rosette-like aggregates, fans, or form thin crusts on the host rock. Its intensely green to yellowish-green color is very characteristic and results from the presence of uranyl ions in its structure. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of about 2.5, meaning it can be scratched with a fingernail. It has a vitreous luster and is transparent to translucent. Its density, approximately 3.25 g/cm³, is relatively high for a non-metallic mineral, which is typical for uranium minerals. ## Colors and Varieties Běhounekite occurs in shades from bright green to yellowish-green. The color variation depends on slight fluctuations in chemical composition and crystallization conditions. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral was officially described and recognized by the International Mineralogical Association (IMA) in 2000. Its name honors František Běhounek (1898–1973), a Czech nuclear physicist, radiologist, and academician, who conducted research on radioactivity in Jáchymov – the mineral's discovery site. ## Applications Due to its extreme rarity and small crystal sizes, běhounekite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for specialized collectors of rare minerals, especially those from the uranium group.
Diagnostic features
## Identification Key diagnostic features of běhounekite include its characteristic bright green color, platy crystal habit with a hexagonal outline, and specific occurrence environment (oxidation zones of uranium deposits, often as a post-mining product). The most important feature is strong radioactivity, easily detectable with a Geiger counter or scintillometer. Unlike many other secondary uranium minerals, běhounekite does not exhibit fluorescence under ultraviolet light. ## Differentiation from similar minerals Běhounekite can be confused with other green, secondary uranium minerals, such as uranopilite, johannite, or zippeite. Uranopilite often forms acicular or fibrous aggregates and exhibits strong green fluorescence under UV. Johannite crystallizes in the triclinic system and also fluoresces. Final differentiation of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Běhounekite forms thin to thick platy crystals, often with a hexagonal habit. These crystals typically occur as small groups, rosette-like or fan-shaped aggregates, as well as thin crusts on the host rock.
Geological environment
## Genesis Běhounekite is a secondary mineral, formed under specific conditions. It forms as a result of the oxidation of uraninite (the main uranium ore) in the presence of sulfate-rich waters. It is often a post-mining mineral, crystallizing on the walls of old mine workings where appropriate humidity and chemical composition of seepage waters prevail. ## Mineral Associations This mineral occurs in association with other secondary sulfates and uranium minerals. Its most common associations include gypsum, uranopilite, zippeite, and johannite. ## Localities The most important and historical occurrence (type locality) is Jáchymov in the Czech Republic, a famous uranium ore mining region. Occurrences are also known in the Blue Lizard Mine in San Juan County, Utah, USA. These are the only confirmed, significant localities for this very rare mineral.
Rarity
Very rare
Collector aspects
## Quality Criteria For collectors, the quality and form of crystal development are most important. Specimens with sharp, well-defined platy crystals forming aesthetic, rosette-like aggregates are most valued. The intensity and purity of the green color also significantly increase the specimen's value. The matrix on which the crystals are embedded, and the presence of rare associated minerals, are also important. ## Popular Localities Specimens from the type locality – Jáchymov in the Czech Republic – are by far the most sought after by collectors. They have historical significance and are considered classic examples of this mineral. Specimens from the Blue Lizard Mine in Utah are also prized, often characterized by attractive aggregates on a light host rock.
Care and storage
## Cleaning Běhounekite is sensitive to water and moisture. Cleaning should only be done dry, using a soft brush to remove dust or, if necessary, compressed air from a safe distance. Any contact with water can lead to dissolution or chemical degradation of the delicate crystals. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. The mineral is sensitive to temperature changes, which can cause its dehydration and destruction. As a highly radioactive mineral, it requires special precautions. Direct skin contact should be avoided, dust should never be inhaled, and hands should always be washed after handling a specimen. ## Storage Běhounekite specimens must be stored in sealed, clearly labeled containers, preferably away from areas of permanent human presence. The use of specialized containers with radiation shielding (e.g., lead-lined) is recommended. It should be isolated from other minerals that may be sensitive to radiation (e.g., smoky quartz, fluorite) to prevent their degradation.