Mendozavilite-NaFe

Chemical formula: [Na<sub>2</sub>(H<sub>2</sub>O)<sub>15</sub>Fe<sup>3+</sup>(H<sub>2</sub>O)<sub>6</sub>][Mo<sup>6+</sup><sub>8</sub>P<sub>2</sub>Fe<sup>3+</sup><sub>3</sub>O<sub>35</sub>(OH)<sub>2</sub>]

Mendozavilite-NaFe is a very rare, hydrated sodium iron phosphomolybdate, forming microscopic, tabular crystals of a yellowish-green color.

## Characteristics Mendozavilite-NaFe is a complex, hydrated sodium iron phosphomolybdate belonging to the mendozavilite group. It occurs as very small, thin, tabular or bladed crystals, rarely exceeding fractions of a millimeter. These crystals often form fan-shaped aggregates, rosettes, or thin coatings and crusts on the surface of the host rock. The mineral is characterized by a vivid yellowish-green to olive-green color. ## Physical Properties The mineral is very soft, with a Mohs hardness of 2. The luster is vitreous, and on cleavage surfaces, it can be pearly. It is transparent to translucent. The density has not been empirically measured but is calculated to be approximately 2.85 g/cm³. ## Colors and Varieties The predominant and only known color of the mineral ranges from yellowish-green to olive-green. No color or commercial varieties are distinguished. ## History and Name The mineral was recognized by the IMA in 1998. Its name refers to its belonging to the mendozavilite group and to the dominant elements – sodium (Na) and iron (Fe) – in its chemical structure. The group name is derived from the name of the Bolivian mining engineer, Eugenio Mendozavil. ## Uses Due to its extreme rarity and occurrence as microscopic crystals, mendozavilite-NaFe has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals and micromounts.

Properties

Mohs hardness
2
Luster
Vitreous, Pearly
Streak
Pale yellow
Density
2.85
Cleavage
Perfect on {010}
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of mendozavilite-NaFe is based on its characteristic yellowish-green color, the form of thin, tabular crystals forming rosettes, and its specific environment of occurrence. Due to the microscopic size of the crystals, a stereoscopic microscope is essential for observation. Final confirmation of identity requires advanced analytical methods, such as EDS spectroscopy. ## Distinguishing from Similar Minerals This mineral is visually almost impossible to distinguish from other members of the mendozavilite group and from some other secondary molybdates, such as betpakdalite. Definitive differentiation is only possible through chemical analysis. ## Crystal Forms It forms very thin, tabular or bladed crystals, often with hexagonal outlines. These crystals typically occur as fan-shaped or radial aggregates, rosettes, as well as coatings and crusts.

Geological environment

## Genesis Mendozavilite-NaFe is a secondary mineral, forming in the oxidation zones of copper-molybdenum deposits, especially in desert climates. It forms as a result of the weathering of primary sulfides, mainly molybdenite. ## Mineral Associations It occurs in association with other secondary minerals of the oxidation zone. At the type locality (Chuquicamata), it is found in association with powellite, lindgrenite, antlerite, brochantite, and gypsum. ## Localities The only confirmed and most important locality for this mineral in the world is the Chuquicamata mine in the Antofagasta region of Chile, which is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The collector's value of mendozavilite-NaFe specimens depends on several factors. Samples with rich, dense aggregates of well-formed, sharp crystals are most highly prized. The intensity and purity of the yellowish-green color are also important. Contrasting matrix and the presence of rare associated minerals enhance its attractiveness. ## Popular Localities All collector specimens of this mineral come from a single location in the world – the Chuquicamata mine in Chile. This is the only source of material available on the market.

Care and storage

## Cleaning Specimens should only be dry-cleaned, using a soft brush or a photographic air blower to remove dust. The mineral is hydrated and very soft, so contact with water and mechanical cleaning are highly inadvisable. ## What to Avoid Avoid contact with water and chemicals, which can damage the delicate crystals. As a hydrated mineral, it is sensitive to high temperatures and dry air, which can lead to dehydration and structural damage. Protect it from direct sunlight and vibrations. ## Storage It is recommended to store specimens in closed, stable conditions, preferably in "micromount" boxes, which protect against dust, mechanical damage, and humidity fluctuations.

Sources

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