Odinite
Chemical formula: (Fe<sup>3+</sup>,Mg,Al,Fe<sup>2+</sup>)<sub>2.5</sub>(Si,Al)<sub>2</sub>O<sub>5</sub>(OH)<sub>4</sub>
Oudinite is a clay mineral from the kaolinite-serpentine group, forming fine-grained, green aggregates, found mainly in marine sediments.
Properties
- Luster
- Dull to earthy
- Streak
- Greenish grey
- Density
- 3.05
- Cleavage
- Perfect on {001}
- Transparency
- Translucent to Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identifying oudinite based on visual characteristics is practically impossible. Reliable identification requires advanced analytical techniques, primarily X-ray diffraction (XRD) and chemical analysis. In the field, its green color, earthy form, and occurrence in a specific geological environment – in shallow-marine sediments rich in green grains – can be an indication. ## Distinguishing from Similar Minerals Oudinite can be easily confused with other green clay minerals, such as glauconite, celadonite, or minerals from the chlorite group (e.g., chamosite). Glauconite usually forms brighter, more lustrous grains. The final distinction of these minerals is possible only by laboratory methods. ## Crystal Forms Oudinite is a cryptocrystalline mineral. It occurs in the form of very fine flakes and lamellae, which form compact, earthy, or dusty aggregates. It often also forms small, spherical or oval aggregates (pellets, ooids) with a diameter of less than a millimeter.
Geological environment
## Genesis Oudinite is an authigenic mineral, meaning it crystallizes directly at the site of sedimentation. It forms during early diagenesis in shallow, tropical marine environments (lagoons, estuaries) with a low rate of sediment accumulation. It is characteristic of the so-called verdine facies. ## Mineral Associations This mineral co-occurs with quartz, calcite, goethite, and other clay minerals. ## Localities The most important and typical occurrence is in the sediments of the Îles de Los off the coast of Guinea. Its presence has also been found in shelf sediments off the coasts of French Guiana, Gabon, and in the Gulf of Guinea.
Rarity
Rare
For collectors
## Quality Criteria Since oudinite does not form aesthetic crystals, its collector's value is mainly related to its scientific and documentary value. Rich, as pure as possible samples from well-described localities, especially from the type locality, are prized. A specimen is more valuable if it has been subjected to analysis confirming its identity (e.g., XRD). ## Popular Localities Oudinite specimens are practically not found on the commercial collector's market. The most sought-after samples come from the type locality in Guinea and are mainly available in the collections of scientific institutions.
Care and storage
## Cleaning Oudinite specimens are extremely delicate and fragile. Wet cleaning should be avoided, as water can cause the aggregate to disintegrate. To remove dust, at most a soft brush or a gentle stream of air from a photographic blower can be used. ## What to Avoid This mineral is sensitive to all mechanical impacts, so touching, scratching, and vibrations should be avoided. It should be protected from contact with water and chemicals. Heating can lead to the loss of structural water and a change in its properties. ## Storage It is recommended to store specimens in closed, stable containers, e.g., "micromount" boxes, which protect against dust, moisture, and mechanical damage.