Leószilárdite

Chemical formula: Na<sub>6</sub>Mg(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(CO<sub>3</sub>)<sub>6</sub>·6H<sub>2</sub>O

Leoszilardite is a very rare, water-soluble uranyl mineral, forming bright yellow, fibrous coatings and crystals.

## Characteristics Leoszilardite is a hydrated sodium, magnesium, and uranyl carbonate. It occurs as small, acicular or fibrous crystals, which often form aggregates, coatings, and crusts on rock surfaces. Due to its nature, specimens are usually small and delicate. The crystals are transparent to translucent and are characterized by a bright yellow color and intense fluorescence under ultraviolet light. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2. It has a vitreous to silky luster, depending on its form of occurrence (single crystals or fibrous aggregates). It is a light mineral. Its most unusual feature is its water solubility, which is rare among minerals. ## Colors and Varieties Leoszilardite occurs in a uniform, bright yellow color. No color varieties or commercial varieties are distinguished for it. ## History and Name The mineral was discovered in the Markey uranium mine in San Juan County, Utah (USA). It was officially recognized by the International Mineralogical Association (IMA) in 2014. Its name honors Leó Szilárd (1899-1964), a Hungarian-American physicist and inventor who played a key role in the development of nuclear energy and was one of the initiators of the Manhattan Project. The name refers to the presence of uranium in the mineral's composition. ## Uses Leoszilardite has no industrial application. Its significance is purely scientific and collectible, as a rare and recently discovered uranium mineral.

Properties

Mohs hardness
~2
Luster
Vitreous
Streak
White
Density
2.457
Cleavage
Perfect on {100}
Fracture
Splintery
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features include its bright yellow color, fibrous or acicular appearance, very low hardness, and strong, greenish-yellow fluorescence under UV light. Its most characteristic, though destructive, feature is its water solubility. ## Distinguishing from Similar Minerals It can be confused with other secondary uranium minerals of similar color and form, such as andersonite, bayleyite, or schröckingerite. Andersonite and bayleyite are also water-soluble but crystallize in different systems (trigonal and monoclinic). Chemical tests or crystallographic analysis are necessary for unambiguous identification. ## Crystal Forms Leoszilardite forms prismatic, acicular crystals elongated along one axis, reaching up to 1 mm in length. Most often, they occur as radial or tangled fibrous aggregates, as well as coatings and crusts.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zone of uranium deposits. It forms as a result of the activity of mine waters in an arid climate, which interact with uranium ores in the presence of carbonates. It originates as an evaporite product on the walls of mine workings. ## Mineral Associations At the type locality (Markey mine, Utah, USA), it co-occurs with gypsum, andersonite, bayleyite, schröckingerite, halite, and probably a new, as yet unnamed uranyl-carbonate mineral. ## Localities The only confirmed occurrence of leoszilardite in the world is its type locality – the Markey mine, Red Canyon, San Juan County, Utah, USA.

Rarity

Very rare

For collectors

## Quality Criteria The quality of leoszilardite specimens is assessed based on the richness and coverage of the host rock surface by crystals. Specimens with visible, well-formed, though microscopic, acicular crystals forming dense aggregates are most valued. Contrast with dark host rock also enhances visual appeal. ## Popular Localities All specimens available on the collector's market come from a single location – the Markey mine in Utah, USA. This is the only known locality for this mineral.

Care and storage

## Cleaning This mineral must absolutely not be cleaned with water or any liquids, as it is soluble in them. The only permissible methods are very careful dust removal with a soft brush or blowing it off with compressed air from a distance. ## What to Avoid Avoid all contact with water, chemical solutions, or even humid air. Storage in a humid environment can lead to slow degradation of the specimen. As a uranium mineral, it emits ionizing radiation – direct exposure should be limited, and it should be stored away from permanently occupied areas. ## Storage Leoszilardite specimens must be stored in a dry, sealed environment. The best solution is sealed "membrane boxes" or containers with a moisture absorber (silica gel). It should be kept at a stable temperature, away from direct sunlight.

External references

Sources

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