Leesite

Chemical formula: K(H<sub>2</sub>O)<sub>2</sub>[(U<sup>6+</sup>O<sub>2</sub>)<sub>4</sub>O<sub>2</sub>(OH)<sub>5</sub>]·3H<sub>2</sub>O

Leesite is a rare, secondary uranyl mineral, forming microscopic, yellow, tabular or bladed crystals.

## Characteristics Leesite is a hydrated potassium uranyl hydroxide, belonging to the rare secondary minerals of uranium deposit oxidation zones. It occurs as very small, usually microscopic crystals with a tabular or bladed habit, which often form radial aggregates, rosettes, or spherulitic clusters. Individual crystals rarely exceed 0.2 mm in length. Due to its chemical composition, this mineral is highly radioactive. ## Physical Properties Leesite crystals exhibit an intense yellow color and a vitreous luster. They are transparent to translucent. The Mohs hardness is estimated at about 2, meaning it is a very soft mineral. The density calculated based on the chemical formula and unit cell parameters is 4.96 g/cm³. ## Colors and Varieties This mineral occurs in a characteristic, light yellow to golden yellow color. No color or commercial varieties have been distinguished. ## History and Name Leesite was first described in 2017 by Travis A. Olds, Jakub Plášil, Anthony R. Kampf, Joe Marti, and Peter C. Burns. The mineral is named in honor of American uranium mineral collector, James "Jim" Lees of Grand Junction, Colorado (USA), who provided the first samples for study. ## Uses Leesite, due to its rarity, microscopic crystal size, and strong radioactivity, has no industrial application. It is solely an object of scientific interest and a collector's item for specialized collectors of uranium minerals.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Light yellow
Density
4.96
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Leesite is identified by its characteristic appearance – light yellow, radial aggregates or rosettes composed of small, tabular crystals. Key diagnostic features include its occurrence in paragenesis with other secondary uranium minerals, strong radioactivity, and characteristic, bright yellow fluorescence under shortwave ultraviolet (UV-SW) light. ## Distinguishing from Similar Minerals Leesite can be confused with many other yellow secondary uranyl minerals, such as metaautunite, uranophane, boltwoodite, or compreignacite. Final and certain distinction from these minerals is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy. ## Crystal Forms Leesite crystals are very small, have a tabular or bladed habit, and are elongated in one direction. They most often form radial, star-shaped aggregates, rosettes, and spherical clusters (spherulites) growing on the host rock.

Geological environment

## Genesis Leesite is a secondary mineral, formed in the oxidation (weathering) zones of uranium deposits. It forms as a result of oxygen-rich waters acting on primary uranium minerals, such as uraninite. It crystallizes in voids and fractures of sedimentary rocks, most commonly sandstones. ## Mineral Associations This mineral co-occurs with other secondary uranium minerals. In the type locality (Blue Lizard mine), it was found in association with gypsum, metazeunerite, uranophane, boltwoodite, compreignacite, and metatorbernite. ## Localities The most important and type locality for leesite is the Blue Lizard mine in San Juan County, Utah (USA). This is, to date, the only confirmed and thoroughly described locality for this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of leesite depends on the richness and aesthetics of the aggregates on the rock matrix. The most prized specimens are those with clearly formed, large (for this mineral) rosettes or spherulites of an intense, golden-yellow color. Contrast with the darker host rock and the absence of damage to delicate crystals are also important. ## Popular Localities The only source of collector specimens is the Blue Lizard mine in Utah, USA. Material from this locality is considered exemplary for this mineral species.

Care and storage

## Cleaning Leesite specimens are generally not cleaned. Any attempts at mechanical or chemical cleaning can irreversibly destroy the delicate, microscopic crystals. If absolutely necessary, dust can be carefully removed with a photographic air blower (non-contact). ## What to Avoid Avoid contact with water, chemicals, ultrasound, and any vibrations or impacts. The crystals are extremely brittle and fragile. As a hydrated mineral, it may be sensitive to changes in humidity and high temperatures, which can lead to its dehydration and destruction. ## Storage Leesite is highly radioactive and must be stored with the utmost caution. It should be kept in a sealed, lead-lined container, away from other minerals (which could be damaged by radiation) and areas of permanent human presence. Storage in specialized "perky box" type containers is recommended to minimize the risk of mechanical damage.

Sources

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