Ewingite

Chemical formula: Mg<sub>8</sub>Ca<sub>8</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>24</sub>(CO<sub>3</sub>)<sub>30</sub>O<sub>4</sub>(OH)<sub>12</sub>·138H<sub>2</sub>O

Ewingite is an extremely rare, complex hydrated uranyl, magnesium, and calcium carbonate, known for forming intensely yellow, radial aggregates of acicular crystals.

## Characteristics Ewingite is a secondary uranium mineral, distinguished by its exceptionally complex chemical composition and crystal structure, which is the most intricate known among all minerals. It forms aggregates of tiny, acicular or hair-like crystals, often arranged in radial forms resembling small hedgehogs or spherical aggregates. Individual crystals are very small, rarely exceeding a millimeter in length, while entire aggregates reach sizes of up to several millimeters. ## Physical Properties Ewingite crystals are very brittle. This mineral exhibits strong, greenish-yellow fluorescence under ultraviolet light (both shortwave and longwave). It is highly radioactive due to its high uranium content. Its hardness and density have not been precisely measured due to the small size and rarity of the crystals. ## Colors and Varieties Ewingite occurs in a characteristic, intense honey-yellow to yellow color. No color or commercial varieties are known. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2016. Its name honors Rodney C. Ewing (born 1946), an American mineralogist and materials scientist from Stanford University, for his significant contributions to uranium mineralogy and nuclear materials research. It was discovered in the dumps of the Plavno uranium mine in the Czech Republic. ## Uses Due to its extreme rarity, small size, and strong radioactivity, ewingite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of uranium minerals.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Pale yellow
Density
3.36
Cleavage
None
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features of ewingite include its intense honey-yellow color, habit in the form of radial aggregates composed of very fine, acicular crystals, and strong greenish-yellow fluorescence under UV light. However, definitive identification is only possible using advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy, due to its resemblance to other secondary uranium minerals. ## Distinguishing from Similar Minerals Ewingite can be confused with other secondary uranyl minerals of similar color and habit, such as studtite, metastudtite, or zippeite. Studtite forms similar acicular aggregates but is a uranyl peroxide and has a different chemical composition. Zippeite often occurs as earthy or powdery coatings, less frequently forming distinct crystals. Final differentiation requires specialized analysis. ## Crystal Forms Ewingite crystallizes in the form of very fine, elongated crystals with an acicular or hair-like habit. These crystals almost always occur in radial, spherical, or hemispherical aggregates, forming characteristic "hedgehogs."

Geological environment

## Genesis Ewingite is a secondary mineral, formed by the weathering and oxidation of primary uranium ores (mainly uraninite) in the presence of waters rich in carbonates, calcium, and magnesium. It forms in the oxidation zones of uranium deposits, most often as coatings and crusts on the walls of mine workings or on the surface of other minerals. ## Mineral Associations This mineral occurs in association with other secondary uranium minerals. At the type locality (Plavno mine), it was found in association with gypsum, uraninite, johannite, schröckingerite, studtite, and metastudtite. ## Localities The only confirmed and described occurrence of ewingite in the world is the dumps of the former Plavno uranium mine in the Ore Mountains (Erzgebirge), near Jáchymov in the Czech Republic.

Rarity

Extremely rare

For collectors

## Quality Criteria The collector's appeal of ewingite is primarily determined by the richness and development of its crystalline aggregates. Specimens with distinct, spherical or radial clusters of acicular crystals, well-separated from the matrix rock, are most valued. Due to the microscopic size of the crystals, the overall size of the aggregate is crucial. A contrasting matrix can enhance the visual value of the specimen. ## Popular Localities The only source of ewingite specimens is its type locality – the Plavno mine in the Czech Republic. All specimens available on the collector's market originate from this single location, making them extremely sought after by specialized collectors of rare and uranium minerals.

Care and storage

## Cleaning This mineral is extremely delicate and brittle. It should not be cleaned mechanically or chemically. Any attempts at cleaning, even with compressed air, can irreversibly damage the specimen. It should be stored in its original state. ## What to Avoid Avoid any contact with water, chemicals, as well as vibrations and shocks. The crystals are sensitive to changes in humidity and temperature. As a highly radioactive mineral, it requires special precautions – direct skin contact, inhalation of dust, and storage in areas of constant human presence should be avoided. ## Storage Ewingite specimens must be stored in specialized, sealed containers (e.g., "perky box" type) that protect them from mechanical damage and dust. Due to radioactivity, they should be kept away from other radiation-sensitive minerals and in a dedicated location, preferably in a lead-lined container, away from living spaces.

External references

Sources

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