Obradovicite-NaNa
Chemical formula: [Na<sub>2</sub>(H<sub>2</sub>O)<sub>16</sub>Na(H<sub>2</sub>O)<sub>6</sub>][Mo<sup>6+</sup><sub>8</sub>As<sup>5+</sup><sub>2</sub>Fe<sup>3+</sup><sub>3</sub>O<sub>33</sub>(OH)<sub>4</sub>]
Obradovicite-NaNa is a very rare sodium iron molybdate arsenate, forming microscopic, tabular crystals of an intensely green color.
Properties
- Mohs hardness
- 2
- Luster
- Vitreous
- Streak
- Light green
- Density
- 3.45
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Triclinic
Diagnostic features
## Identification In practice, the identification of this mineral relies on its unique appearance and geological context. Characteristic features include its intensely green color, vitreous luster, and occurrence as small, tabular crystals forming rosette-like aggregates on the host rock. Final confirmation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other secondary, green arsenic minerals, such as agardite, annabergite, or olivenite. However, it is distinguished by its specific crystal habit (thin tabular crystals in rosettes) and its co-occurrence with molybdenite and other molybdates in the oxidation zone. Most similar minerals form acicular or prismatic crystals. ## Crystal Forms Crystals are very small, thin, and tabular, with a hexagonal or platy outline. They typically form radial or rosette-like aggregates, as well as thin coatings on the rock surface.
Geological environment
## Genesis Obradovicite-NaNa is a secondary mineral, formed in the oxidation zones of molybdenum-copper deposits. It forms as a result of the weathering of primary sulfides, mainly molybdenite and pyrite, in the presence of arsenic minerals. ## Mineral Associations It most commonly co-occurs with quartz, molybdenite, pyrite, chalcopyrite, tenorite, hematite, jarosite, as well as other rare molybdates such as wulfenite and lindgrenite. ## Localities The only confirmed locality for this mineral in the world (type locality) is the abandoned Chuquicamata copper and molybdenum mine, located in the Atacama Desert in the Antofagasta region of Chile.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of Obradovicite-NaNa specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. The most prized samples are those with clearly formed, undamaged rosettes of an intensely green color, contrasting well with the light host rock (most often quartz). Crystal size, although always microscopic, is also important – larger and better-formed tabular crystals increase the value of the specimen.
Care and storage
## Cleaning Due to the extreme rarity and delicate nature of specimens, mechanical cleaning is absolutely inadvisable. Contact with water and any chemicals should be avoided. The safest method is to remove dust using compressed air from a safe distance. ## What to Avoid Vibrations, shocks, ultrasound, and any attempts at chemical or mechanical cleaning should be avoided. Specimens are sensitive to changes in humidity and temperature. They should not be exposed to direct sunlight. ## Storage Obradovicite-NaNa specimens should be stored exclusively in specialized, sealed "micromount" boxes, protecting them from dust, humidity, and mechanical damage. Store under stable room conditions.