Rabejacite
Chemical formula: Ca<sub>2</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>4</sub>O<sub>4</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O
Rabejacite is a rare, secondary uranium mineral, forming golden-yellow crusts and aggregates of small, tabular crystals.
Description
## Characteristics Rabejacite is a hydrated uranyl calcium sulfate hydroxide. It occurs as crusts, coatings, or spherulitic aggregates composed of very small, tabular crystals. Its most characteristic feature is its intense, golden-yellow color. Crystals are usually too small to be observed with the naked eye, forming microcrystalline clusters on the surface of the host rock. ## Physical properties This mineral has a vitreous luster and is translucent. Its hardness has not been determined, but due to its form and composition, it is a very brittle and soft mineral. Density has also not been measured, only calculated to be over 4.2 g/cm³. As a uranium mineral, rabejacite is highly radioactive. ## Colors and varieties Rabejacite's color is uniform, ranging from golden-yellow to orange-yellow. No color or commercial varieties are distinguished. ## History and name The mineral's name, given in 1993 by Michel Deliens and Paul Piret, comes from its discovery site - the Rabejac uranium deposit, located near Lodève in the Hérault department, France. ## Applications Rabejacite has no industrial applications. Due to its rarity, attractive color, and interesting origin, it is a sought-after and valued mineral by collectors specializing in uranium minerals.
Diagnostic features
## Identification Key diagnostic features of rabejacite are its intensely golden-yellow color, occurrence as microcrystalline crusts, and strong radioactivity. Co-occurrence with other secondary uranium minerals in oxidation zones of deposits is also an important indicator. ## Distinguishing from similar minerals Rabejacite can be confused with other yellow uranyl minerals, such as zippeite, uranopilite, or meta-autunite. Zippeite forms similar aggregates but often has a slightly different hue. Uranopilite can be more greenish-yellow and exhibits stronger fluorescence under UV light. Certain distinction of these minerals is often impossible without advanced studies, such as chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal forms Rabejacite forms aggregates of very fine, thin, tabular crystals, flattened along one plane. These clusters are most often radial, spherulitic, or form thin coatings on the host rock.
Geological environment
## Genesis It is a secondary mineral, formed in the oxidation (weathering) zones of uranium deposits, most often in sedimentary rocks, such as sandstones. It forms as a result of the action of acidic, sulfate-rich waters on primary uranium minerals (e.g., uraninite) in the presence of calcium. ## Mineral associations It most often co-occurs with other secondary uranium minerals, such as gypsum, uranopilite, zippeite, schröckingerite, and uranophane. ## Localities The most important occurrences of this rare mineral are the type locality - the Rabejac deposit near Lodève in France. Significant specimens also come from the Blue Lizard mine in San Juan County, Utah, USA. Occurrences have also been reported in Saxony, Germany, including the Johanngeorgenstadt area.
Rarity
Very rare
Collector aspects
## Quality criteria The collector's appeal of a specimen depends on the richness and intensity of the rabejacite crusts' color. Samples with well-formed, though still microscopic, crystalline aggregates covering a significant area of contrasting host rock are most valued. Co-occurrence with other rare uranium minerals also increases value. ## Popular localities The best specimens in the world are considered to be those from the Blue Lizard mine in Utah (USA), which are distinguished by exceptionally rich and brightly colored clusters. Samples from the type locality in France are also highly valued.
Care and storage
## Cleaning Rabejacite specimens are extremely delicate and brittle. Mechanical cleaning and contact with water, which can damage the mineral's hydrated structure, should be avoided. For dust removal, it is best to use a soft brush or a stream of compressed air from a safe distance. ## What to avoid The mineral is sensitive to moisture, chemicals, and mechanical damage. It should be protected from impacts and scratches. As a radioactive mineral, it requires careful handling - hands should be washed after each contact. It should not be stored in places of permanent human presence. ## Storage It is recommended to store specimens in a dry place, preferably in closed, transparent containers (so-called perky boxes), which protect against dust and damage. Due to radioactivity, specimens should be kept in a designated area, away from other radiation-sensitive minerals and away from bedrooms or living rooms. The container should be marked with a radioactivity symbol.