Albrechtschraufite
Chemical formula: Ca<sub>4</sub>Mg(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(CO<sub>3</sub>)<sub>6</sub>F<sub>2</sub>·17H<sub>2</sub>O
Albrechtschraufite is a very rare, secondary uranium mineral, forming yellow, strongly fluorescent coatings and crusts in mines.
Description
## Characteristics Albrechtschraufite is a hydrated uranyl, calcium, and magnesium carbonate. It occurs as delicate, brittle coatings and crusts on the walls of mine workings. It forms aggregates of small, bladed or acicular crystals, which rarely reach macroscopic sizes. It is usually observed as microcrystalline aggregates. It is a secondary mineral, formed by the weathering processes of primary uranium ores. ## Physical Properties This mineral is very soft, with a Mohs hardness of about 2-3. Its luster is described as vitreous, becoming pearly on planes of perfect cleavage. It is transparent to translucent. A characteristic feature is its instability in dry air – it readily loses crystallization water and decomposes (effloresces). ## Colors and Varieties Albrechtschraufite ranges in color from yellow to greenish-yellow. No named varieties are distinguished. ## History and Name The mineral is named in honor of Albrecht Schrauf (1837–1897), professor of mineralogy at the University of Vienna and curator of the mineralogical collection at the Natural History Museum in Vienna. It was described as a new mineral species in 1985 based on material collected from the historic uranium mine in Jáchymov, Czech Republic. ## Uses Due to its extreme rarity, small crystal size, and instability, albrechtschraufite has no industrial applications. It is of purely scientific and collector interest, being a coveted item for specialists collecting uranium minerals.
Diagnostic features
## Identification The key diagnostic feature of albrechtschraufite is its very strong, bright green fluorescence under ultraviolet light (both shortwave and longwave). Its yellow color, occurrence as delicate coatings in uranium mines, and radioactivity are also important indicators. It is an unstable mineral in dry air. ## Distinguishing from Similar Minerals It can be confused with other secondary uranium minerals of similar color and fluorescence, such as liebigite, andersonite, or schröckingerite. Liebigite crystallizes in the orthorhombic system and has a slightly different crystal habit. Andersonite forms granular aggregates and crystallizes in the trigonal system. Definitive differentiation of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms aggregates of small, bladed or fibrous crystals. Most commonly, it occurs as ephemeral, powdery or earthy coatings and crusts on host rocks.
Geological environment
## Genesis Albrechtschraufite is a secondary mineral, formed in the oxidation zone of uranium deposits. It forms contemporaneously (it is a post-mining mineral) on the walls of damp mine workings as a result of the reaction of carbonate- and sulfate-rich waters with primary uraninite. It crystallizes from aqueous solutions under the specific microclimatic conditions prevailing in mines. ## Mineral Associations It most commonly co-occurs with other secondary, water-soluble uranium minerals, such as liebigite, schröckingerite, andersonite, and also with gypsum. ## Localities This is a very rare mineral. The most important and classic locality for its occurrence, from which the type material originates, is Jáchymov (formerly St. Joachimsthal) in the Czech Republic. It is also known from several other uranium mines worldwide where similar conditions prevail.
Rarity
Very rare
Collector aspects
## Quality Criteria The quality of albrechtschraufite specimens is primarily assessed based on the richness and surface coverage of the host rock by the mineral. Specimens with vibrant, intensely yellow coloration and those that reveal well-formed, though still small, crystalline forms under the microscope are most highly valued. Strong fluorescence is standard for this mineral, but its intensity can enhance the attractiveness of a specimen. Due to its nature, specimens are usually small (so-called "micromounts"). ## Popular Localities The only classic and widely known source of collector specimens is the historic mining district of Jáchymov in the Czech Republic.
Care and storage
## Cleaning The mineral is extremely sensitive. It must absolutely not be cleaned with water or any liquids, as it is partially soluble and readily loses structural water, leading to its disintegration. Only very careful dust removal with a soft, dry brush or a gentle stream of compressed air from a distance is permissible. ## What to Avoid Avoid contact with water and chemicals, sudden changes in temperature and humidity, and exposure to dry air. As a uranium mineral, it is radioactive and requires proper handling – avoid direct skin contact, do not inhale dust, and wash hands after each contact. Store away from areas of permanent human presence. ## Storage Albrechtschraufite specimens should be stored in sealed, airtight containers (e.g., "perky boxes") to maintain stable humidity and prevent water loss (efflorescence). The container also protects against dusting and shields the surroundings from radiation. It should be stored away from other minerals that may be sensitive to radiation.