Wetherillite

Chemical formula: Na<sub>2</sub>Mg(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>4</sub>·18H<sub>2</sub>O

Wetherillite is a very rare, water-soluble hydrated uranyl, sodium, and magnesium sulfate, forming aggregates of microscopic, acicular crystals.

## Characteristics Wetherillite is a sulfate mineral belonging to the secondary uranium minerals. It occurs as aggregates of extremely small, acicular or bladed crystals, rarely exceeding 1 mm in length. Individual crystals are usually colorless, but in aggregates, they appear white or have a very pale, yellowish-green hue. Due to its chemical composition, this mineral exhibits intense, green fluorescence under shortwave ultraviolet (UV-SW) light. ## Physical Properties Wetherillite crystals are extremely delicate and brittle. The mineral is characterized by a vitreous luster. Its hardness and density have not been precisely measured due to the small size and fragility of the crystals; however, the density calculated based on the chemical formula and unit cell parameters is approximately 2.75 g/cm³. It is a strongly radioactive mineral. ## Colors and Varieties This mineral is typically colorless, and its aggregates appear white. Sometimes a very light, yellowish-green hue is observed. No color or commercial varieties have been distinguished. ## History and Name The name wetherillite was given in honor of Charles Mayer Wetherill (1825–1871), an American chemist and mineralogist who first described and studied many uranium minerals from Pennsylvania, including those from the johannite group. The mineral was formally described and approved by the International Mineralogical Association (IMA) in 2018 (IMA2018-058). Type specimens come from the Blue Lizard Mine in San Juan County, Utah, USA. ## Uses Wetherillite has no industrial applications. Due to its extreme rarity, microscopic crystal sizes, and scientific significance, it is of interest only to specialized collectors of uranium minerals and research institutions.

Properties

Luster
Vitreous
Streak
White
Density
2.75
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification A key diagnostic feature of wetherillite is its intense green fluorescence under shortwave UV light. Its occurrence as fine, acicular crystals forming crusts and coatings also aids identification. However, confirmation of identity requires advanced analytical methods such as Raman spectroscopy or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other secondary uranyl sulfates, such as natrozippeite, johannite, or gypsum. It is distinguished from gypsum by its significantly higher radioactivity and strong fluorescence. Distinguishing it from other uranyl sulfates based on visual characteristics is practically impossible and requires specialized laboratory analyses. ## Crystal Forms Wetherillite forms very small, elongated crystals with an acicular or bladed habit. They occur as radial aggregates, tangled felt-like masses, or as fine coatings and crusts on the host rock.

Geological environment

## Genesis Wetherillite is a secondary uranium mineral that forms in the oxidation zone of uranium-vanadium deposits. It crystallizes as a result of the evaporation of mine waters rich in dissolved uranyl, sulfate, sodium, and magnesium ions. It forms contemporaneously on the walls and ceilings of mine workings in a dry, desert climate. ## Mineral Associations This mineral co-occurs with other secondary sulfates and uranyl sulfates, such as johannite, natrozippeite, epsomite, hexahydrite, and also with gypsum. ## Localities The only confirmed locality of wetherillite in the world (type locality) is the Blue Lizard Mine, located in Red Canyon, San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria For collectors, the abundance and richness of the mineral's occurrence on the rock matrix are most important. Specimens with visible, well-formed crystalline aggregates are valued, even if individual crystals are microscopic. Color contrast with the substrate and fluorescence intensity also increase the specimen's value. Due to the nature of the mineral, the purity and size of individual crystals are not key criteria. ## Popular Localities The only source of wetherillite specimens is the Blue Lizard Mine in Utah, USA. All materials available on the collector's market originate from this single locality.

Care and storage

## Cleaning Wetherillite specimens must absolutely not be wet cleaned. The mineral is water-soluble, and contact with water, even in the form of humidity, leads to its destruction. To remove dust, only compressed air from a safe distance or a very soft brush should be used, with the utmost caution. ## What to Avoid Contact with water, water vapor, and high air humidity must be strictly avoided. It must be protected from all chemicals, acids, and cleaning agents. The crystals are extremely brittle, so shocks, vibrations, and touching should be avoided. ## Storage Wetherillite must be stored in a dry, airtight container, preferably with a desiccant (e.g., silica gel). As a radioactive mineral, it should be kept away from other radiation-sensitive minerals, in a place inaccessible to children and animals, in accordance with local regulations for storing radioactive materials.

Sources

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