Leydetite
Chemical formula: Fe<sup>2+</sup>(U<sup>6+</sup>O<sub>2</sub>)(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·11H<sub>2</sub>O
Leydetite is a very rare secondary mineral from the uranyl sulfate group, forming tiny, yellow crystals in uranium mines.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous to Pearly
- Streak
- Pale yellow
- Density
- 3.03
- Cleavage
- Perfect on {010}
- Transparency
- Transparent to Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Characteristic features of leydetite include its bright yellow color, specific form of thin, tabular crystals forming aggregates, and occurrence in paragenesis with other secondary uranium minerals. Key diagnostic features are strong radioactivity and intense, yellowish-green fluorescence under ultraviolet light (both short- and long-wave). ## Distinguishing from Similar Minerals Leydetite can be confused with other yellow, secondary uranium minerals, such as uranopilite, zippeite, or johannite. Distinguishing it based on visual features is very difficult and often impossible without advanced studies, such as X-ray diffraction (XRD) or chemical analysis. Observation of crystal form and precise color can be helpful. ## Crystal Forms It forms thin, bladed or tabular crystals, elongated along one axis. These crystals aggregate into spherical clusters, rosettes, or form coatings and crusts.
Geological environment
## Genesis Leydetite is a secondary mineral, forming in the oxidation zones of uranium deposits. It forms in post-mining conditions, as a result of the weathering of uraninite in the presence of iron sulfides (pyrite, marcasite) in a humid environment, most often on the walls of old mine workings. ## Mineral Associations It most often co-occurs with other secondary uranyl sulfates, such as uranopilite and zippeite. It is also accompanied by gypsum, pyrite, marcasite, and primary uraninite. ## Localities The most important and type locality is the Rabejac uranium mine near Lodève (Hérault, Occitanie) in France. It is also known from the Krunkelbach mine in the Black Forest (Baden-Württemberg) in Germany.
Rarity
Very rare
For collectors
## Quality Criteria As a mineral occurring mainly in the form of microscopic specimens (so-called micromounts), rich aggregates of well-formed, sharp crystals are most highly valued. The intensity of the color and the aesthetic arrangement on a small fragment of the host rock are also important. Specimens with well-identified associated minerals are additionally valued. ## Popular Localities The most known and valued specimens come from the type locality – the Rabejac mine in France. This is the main source of this mineral for collectors.
Care and storage
## Cleaning Leydetite specimens are extremely delicate and sensitive to water. Cleaning should only be done dry, using a soft brush or compressed air to remove dust. Any contact with water and chemical agents should be avoided. ## What to Avoid The mineral is sensitive to changes in humidity and temperature, which can lead to its dehydration and disintegration. It should be protected from direct sunlight, moisture, and high temperatures. As a radioactive mineral, it requires careful handling – avoid inhaling dust and wash hands after each contact. ## Storage It is recommended to store specimens in sealed, airtight containers (e.g., "perky box" type) to stabilize humidity. The container should be clearly labeled as radioactive material. It should be kept away from other radiation-sensitive minerals and away from areas of permanent human habitation.