Metavandendriesscheite
Chemical formula: Pb²⁺U⁶⁺₇O₂₂·nH₂O
Metavandendriesscheite is a rare, secondary uranium mineral, forming microscopic, tabular crystals of an intense orange or yellowish-orange color.
Properties
- Mohs hardness
- 3
- Color
- Amber-yellow, yellowish orange, orange
- Luster
- Vitreous to adamantine, dull
- Streak
- Light yellow
- Density
- 5.45
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Key diagnostic features include its intense orange color, occurrence in the oxidation zones of uranium deposits, characteristic crystal forms (small tabular crystals, rosettes), and strong radioactivity, easily detectable with a Geiger counter. Under shortwave UV light, it exhibits weak, green fluorescence. ## Distinguishing from Similar Minerals It can be confused with other secondary uranyl minerals of similar color, such as fourmarierite, wölsendorfite, or vandendriesscheite itself. Final differentiation requires advanced analytical methods, such as X-ray diffraction (XRD), due to subtle differences in crystal structure and chemical composition. ## Crystal Forms Crystals are very small, tabular in habit, flattened parallel to {001}. They often form radial or stellate aggregates, as well as thin coatings and crusts on rock surfaces.
Geological environment
## Genesis Metavandendriesscheite is a secondary mineral, forming in the oxidation (weathering) zones of uraninite and other primary uranium minerals. It forms as a result of dehydration of vandendriesscheite under conditions of low air humidity. It is a product of alteration of hydrothermal veins containing uraninite. ## Mineral Associations It most commonly co-occurs with minerals from which it forms or which it accompanies during weathering. These include primarily uraninite, vandendriesscheite, fourmarierite, masuyite, rutherfordine, kasolite, curite, and wölsendorfite. ## Localities The most important and classic locality is the Shinkolobwe mine in Haut-Katanga Province, Democratic Republic of Congo, from which the best-formed specimens originate. It is also known from several other localities worldwide, including the Ruggles mine in Grafton, New Hampshire (USA) and the Lake Athabasca region in Saskatchewan (Canada).
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued specimens are those with well-formed, sharp microcrystals forming aesthetic, radial aggregates or rosettes. The intensity and saturation of the orange color also increase value. Contrast with the rock matrix and the presence of rare associated minerals are important. Due to the microscopic size of the crystals, specimens are evaluated primarily under magnification. ## Popular Localities Specimens from the type locality – the Shinkolobwe mine in the DRC – are by far the most sought after by collectors. Material from this location is considered the global standard for this mineral.
Care and storage
## Cleaning Specimens of this mineral should generally not be wet cleaned. Only gentle dust removal with a soft brush or a photographic air blower is permissible. Contact with water can lead to rehydration and transformation into other uranyl minerals. ## What to Avoid Contact with water and chemicals must be strictly avoided. The mineral is sensitive to changes in humidity. As a secondary mineral, it is unstable under conditions other than those in which it formed. It should be protected from direct sunlight, which can cause fading, and from high temperatures. ## Storage Metavandendriesscheite is strongly radioactive. It should be stored in specialized lead containers or in thick plastic boxes, away from other radiation-sensitive minerals. The container must be clearly marked with a radioactivity symbol. Store in a dry place, away from people and animals, preferably in a dedicated collection of radioactive minerals.