Agrinierite
Chemical formula: K<sub>2</sub>Ca[(U<sup>6+</sup>O<sub>2</sub>)<sub>3</sub>O<sub>3</sub>(OH)<sub>2</sub>]<sub>2</sub>·5H<sub>2</sub>O
Agrinierite is a very rare, highly radioactive secondary uranium mineral, forming characteristic, tabular crystals of an intense orange color.
Properties
- Luster
- Resinous to sub-adamantine
- Streak
- Pale orange
- Density
- 5.63
- Cleavage
- Perfect on {100}
- Transparency
- Translucent to opaque
- Crystal system
- Orthorhombic
Diagnostic features
## Identification The key diagnostic feature of agrinierite is its strong radioactivity, easily detectable with a Geiger-Müller counter. Other helpful identification features include its characteristic orange color, tabular crystal habit, and occurrence in association with other secondary uranium minerals. ## Distinguishing from Similar Minerals Agrinierite can be confused with other orange or red uranyl minerals, such as becquerelite, fourmarierite, or wölsendorfite. These minerals often co-occur and have a similar appearance. Definitive distinction is usually only possible using advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Crystal Forms Agrinierite crystallizes in the orthorhombic system, forming very thin, tabular or bladed crystals, often elongated in one direction. These crystals usually occur as radial or stellate aggregates, rosettes, and thin crusts.
Geological environment
## Genesis Agrinierite is a secondary mineral, formed in the oxidation (weathering) zones of uranium deposits. It forms as a result of hydrothermal or supergene alteration of uraninite in an environment rich in potassium and calcium. ## Mineral Associations It most commonly co-occurs with primary uraninite and other secondary uranium minerals, such as becquerelite, fourmarierite, uranophane, schoepite, and curite. ## Localities It is a very rare mineral, known from only a few localities worldwide. The most important and classic locality is the Margnac mine in Compreignac, France. It has also been reported from the Rössing uranium mine in Namibia.
Rarity
Very rare
For collectors
## Quality Criteria The most highly prized agrinierite specimens are characterized by sharp, well-formed crystals of a vivid, intensely orange color. The aesthetics of the aggregates (e.g., perfectly formed rosettes) and their placement on a contrasting host rock are important. Due to the typically microscopic size of the crystals, specimens with visible, larger crystals are exceptionally sought after. ## Popular Localities Specimens from the type locality – the Margnac mine in France – are considered the best in the world. They serve as a benchmark for this mineral and are the most desired by specialized collectors.
Care and storage
## Cleaning Agrinierite specimens are extremely delicate and brittle. They must not be cleaned mechanically or with water or other liquids. Only very careful dust removal using a low-pressure stream of compressed air is permissible. ## What to Avoid Contact of the mineral with skin and inhalation of dust must be strictly avoided due to its high radioactivity. Hands should be thoroughly washed after any potential contact. The mineral is very soft and brittle, so it must be protected from any impacts, vibrations, and abrasions. It should not be heated or exposed to chemicals. ## Storage Agrinierite must be stored in specialized, sealed containers that limit radiation emission, e.g., in lead-lined boxes or those made of thick acrylic. The container must be clearly marked with the international radioactivity symbol. It should be kept in an area isolated from living spaces and away from other minerals that may be damaged by radiation (e.g., smoky quartz, fluorite, topaz).