Obradovicite-NaCu

Chemical formula: [Na<sub>2</sub>(H<sub>2</sub>O)<sub>17</sub>Cu<sup>2+</sup>(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>34</sub>(OH)<sub>3</sub>]

Obradovicite-NaCu is a very rare, complex molybdate with an intensely green color, occurring as tiny, acicular crystals.

## Characteristics Obradovicite-NaCu is an extremely rare secondary mineral from the obradovicite group. It forms aggregates of very small, acicular or capillary crystals, which can form radial aggregates or coatings. Its most characteristic feature is its vibrant, intensely green color. ## Physical Properties Crystals are flexible and exhibit a luster ranging from vitreous to silky. Due to the small size of the crystals, most physical properties, such as hardness or density, are difficult to measure precisely and have been estimated. ## Colors and Varieties This mineral occurs in shades from green to yellowish-green. No varieties are known. ## History and Name It was named after Martin Obradovic (born 1958), a mineral collector from New York, who provided the first samples for research. The suffix "-NaCu" refers to the dominant cations in its structure. The mineral was approved by the IMA in 2008. The type locality is the Chuquicamata mine in Chile. ## Uses Obradovicite-NaCu has no industrial application. It is solely an object of interest for collectors specializing in rare minerals and scientists studying complex molybdenum compounds.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Light green
Density
2.83
Cleavage
Perfect on {010}
Fracture
Splintery
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification is based on its characteristic form (tiny, acicular crystals in radial aggregates), intensely green color, and co-occurrence with other secondary molybdates and sulfates in the oxidation zones of copper deposits. ## Differentiation from Similar Minerals It can be confused with other green secondary minerals, such as brochantite, malachite, or other rare molybdates. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or electron spectroscopy (EDS), due to its unique chemical composition. ## Crystal Forms It forms very small, acicular or capillary crystals, usually grouped into radial aggregates, rosettes, or forming thin coatings and crusts on the host rock.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones of hydrothermal polymetallic deposits rich in molybdenum, copper, and arsenic. It crystallizes from aqueous solutions under conditions of strong weathering. ## Mineral Associations It most often occurs in association with tenorite, lindgrenite, hematite, quartz, and also other rare molybdates, such as obradovicite-KCu or powellite. ## Localities The only confirmed and described occurrence of this mineral in the world is the Chuquicamata copper mine, located in the Antofagasta region of Chile.

Rarity

Extremely rare

For collectors

## Quality Criteria The most valuable specimens are those that possess well-formed, even if microscopic, radial aggregates of an intense, vivid green color, contrasting with the rock matrix. Due to its rarity, any well-documented specimen is valuable. ## Popular Localities The only source of specimens is the Chuquicamata mine in Chile, which makes them highly sought after by collectors specializing in type locality minerals and systematic collections.

Care and storage

## Cleaning Mechanical cleaning should be avoided. If absolutely necessary, compressed air can be used from a safe distance to remove dust. Contact with water or other liquids is not recommended. ## What to Avoid The mineral is extremely delicate. Touching, vibrations, ultrasonics, and any chemicals should be avoided. Samples should be protected from sudden changes in temperature and humidity. ## Storage Specimens should be stored under stable conditions, in sealed "micromount" containers, to protect them from mechanical damage and dust. They should not be exposed to direct sunlight.

Sources

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