Hydronováčekite
Chemical formula: Mg(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>·12H<sub>2</sub>O
Hydronováčekite is a rare, secondary uranium mineral of the autunite group, forming small, yellowish-green crystals with strong fluorescence under UV light.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous, Pearly
- Streak
- Pale yellow
- Density
- 3.35
- Cleavage
- Perfect on {001}
- Fracture
- Micaceous
- Transparency
- Transparent to translucent
- Crystal system
- Tetragonal
Diagnostic features
## Identification A key diagnostic feature is its very intense, yellowish-green fluorescence under shortwave and longwave ultraviolet (UV) light. Its characteristic pale yellow to yellowish-green color, tabular crystal habit, and association with other secondary uranium minerals also aid in identification. ## Distinguishing from Similar Minerals It can be confused with other minerals from the autunite group, such as autunite, torbernite, zeunerite, or nováčekite. Distinguishing it from nováčekite is particularly difficult and often requires advanced analytical methods (e.g., XRD) to determine the degree of hydration. It differs from autunite by the presence of arsenic instead of phosphorus, and from zeunerite by the presence of magnesium instead of copper, which, however, is not visually discernible. ## Crystal Forms It forms thin, square or rectangular tabular crystals. These crystals often arrange into fan-like, radial, or rosette aggregates. It also occurs as microcrystalline masses, coatings, and crusts.
Geological environment
## Genesis It is a secondary mineral, forming in the oxidation zones (weathering) of hydrothermal and sedimentary uranium deposits containing arsenic. It crystallizes from waters rich in uranium, magnesium, and arsenic under conditions of low temperature and pressure. ## Mineral Associations It co-occurs with other secondary uranium minerals, such as uraninite (as a primary mineral), nováčekite, arsenuranospathite, uranophane, zeunerite, and gypsum. ## Localities The most important localities worldwide include the Clara mine in Wolfach (Black Forest, Germany), which is the type locality. It is also known from Weisser Hirsch in Schneeberg (Saxony, Germany) and from Jáchymov in the Czech Republic.
Rarity
Very rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals creating aesthetic, fan-like or rosette aggregates. The intensity of the color and the contrast with the rock matrix are important. Due to the small size of the crystals, specimens visible to the naked eye are rare and sought after. ## Popular Localities The best quality specimens, considered the global standard for this mineral, come from the Clara mine in Germany.
Care and storage
## Cleaning Specimens should not be wet cleaned. Only gentle dust removal with a soft brush or compressed air from a safe distance is permissible. ## What to Avoid Contact with water must be absolutely avoided, as it can damage and dissolve the crystals. 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 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, transparent containers (e.g., "perky boxes") that protect against mechanical damage and humidity changes. Due to radioactivity, specimens should be kept away from areas of constant human presence, in a well-ventilated room.