Abernathyite

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

Abernathyite is a rare, radioactive uranium mineral with an intensely yellow color and strong fluorescence, forming platy crystals.

## Characteristics Abernathyite is a hydrated potassium uranyl arsenate, belonging to the autunite group. It forms characteristic, thin to thick, platy crystals with a square outline, which often arrange into rosette-like aggregates or form crusts and coatings. Its most striking feature is its bright yellow color. It is a secondary mineral, forming in the oxidation zones of uranium deposits. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2.5-3. It exhibits perfect cleavage in one direction, making it brittle and susceptible to mechanical damage. The luster on fresh surfaces is vitreous, while on cleavage planes it becomes pearly. It is transparent to translucent. Its density ranges from 3.34 to 3.49 g/cm³. A key physical property is its strong radioactivity and intense, yellow-green fluorescence under ultraviolet light (both shortwave and longwave). ## Colors and Varieties Abernathyite occurs almost exclusively in shades of bright, lemon yellow. No color varieties or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Jess Abernathy, an American mineral prospector from Moab, Utah, who found the first specimens. It was described as a new mineral species in 1956 by M. E. Thompson, Blanche Ingram, and E. B. Gross. The type locality is the Fuemrol No. 2 mine in the San Rafael district, Emery County, Utah, USA. ## Uses Due to its rarity and occurrence in small quantities, abernathyite has no industrial application. It is solely an object of scientific interest and a prized collector's mineral, especially among uranium mineral collectors.

Properties

Mohs hardness
2.5-3
Luster
Vitreous, pearly
Streak
Pale yellow
Density
3.34-3.49
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Tetragonal

Diagnostic features

## Identification The most important diagnostic features of abernathyite are its bright yellow color, platy crystal habit with a square cross-section, and perfect cleavage in one direction. A key test is to check for fluorescence – this mineral exhibits a very strong, yellow-green glow under UV light. Its radioactivity, detectable with a Geiger counter, also serves as confirmation. ## Distinguishing from Similar Minerals Abernathyite can be confused with other yellow secondary uranium minerals, such as autunite, uranophane, or zeunerite. It differs from autunite in its chemical composition (arsenic instead of phosphorus) and often slightly different shades of fluorescence, although they can be similar. Uranophane typically forms acicular or fibrous aggregates, not platy crystals. Zeunerite, although having a similar crystal form, is usually green. ## Crystal Forms Abernathyite crystallizes in the tetragonal system, forming thin or thick plates with a square outline. Crystals often occur as single flakes on the matrix rock or form fan-like and rosette-like aggregates. It is also found in the form of fine-grained crusts.

Geological environment

## Genesis Abernathyite is a secondary mineral, forming in the oxidation (weathering) zones of uranium deposits. It forms as a result of groundwater containing dissolved oxygen and arsenic acting on primary uranium minerals, such as uraninite. It most commonly occurs in uranium-impregnated sandstone deposits. ## Mineral Associations This mineral often co-occurs with other arsenates and secondary minerals of the oxidation zone. Its typical associations include scorodite, zeunerite, heinrichite, nováčekite, and relics of primary uraninite. ## Localities The most important abernathyite localities worldwide include historical sites in the USA (Fuemrol mine in Utah), France (Liauzun in Auvergne; Riviéral near Lodève), Germany (Johanngeorgenstadt and Schneeberg in Saxony), and Poland (uranium mine in Kletno in the Śnieżnik Massif).

Rarity

Rare

For collectors

## Quality Criteria The most highly valued abernathyite specimens are characterized by sharply defined, well-formed crystals with an intense, pure yellow color. Crystal size is of great importance – specimens with flakes several millimeters across are already considered very good. The attractiveness is also enhanced by a contrasting matrix rock and the presence of associated minerals. Rich, druzy crusts with vivid color and strong fluorescence are also sought after by collectors. ## Popular Localities European localities, especially from France (Liauzun, Riviéral) and Germany (Johanngeorgenstadt), are considered classic and yield the best specimens, renowned for their sharp microcrystals. Specimens from the type locality in Utah (USA) are mainly of historical significance.

Care and storage

## Cleaning Abernathyite is a brittle mineral and sensitive to water. It should only be cleaned dry, using a soft brush to remove dust or a gentle stream of compressed air. Contact with water can lead to its damage or alteration into other secondary minerals. ## What to Avoid Contact with water, acids, and other chemicals should be strictly avoided. The mineral is sensitive to shocks and impacts due to its perfect cleavage. As a uranium mineral, it is radioactive, so direct contact should be minimized, and hands should always be washed after handling. It should not be stored in areas of high humidity. ## Storage Abernathyite specimens must be stored with precautions for radioactive minerals. It is recommended to keep them in sealed, labeled containers (e.g., thick plastic or lead-lined), in a well-ventilated area, away from permanent human presence, especially bedrooms. Display should be behind a barrier, such as in a closed display case.

External references

Sources

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