Uroxite

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

Uroxite is an extremely rare, secondary uranyl mineral, distinguished by its intense yellow color and occurrence as microscopic crystals.

## Characteristics Uroxite is a hydrated uranyl hydroxyoxalate. It forms very small, bladed or acicular crystals, rarely exceeding 0.2 mm in length. They typically occur as radial or tangled aggregates, as well as coatings and efflorescences on the host rock. Due to their size, individual crystals are most often observable only under a microscope. ## Physical Properties Uroxite crystals exhibit an intensely yellow luster, described as vitreous to silky. They are transparent to translucent. Hardness and density have not been precisely measured due to the small size and rarity of the material; however, the density calculated based on the formula and cell parameters is 3.59 g/cm³. ## Colors and Varieties This mineral occurs in a characteristic, intense yellow color. No color varieties or commercial varieties are known. ## History and Name Uroxite was first described in 2014 by Travis A. Olds and co-workers. Its name is derived from the combination of the Latin words *uranium* and *oxalate*, directly referring to its chemical composition. It was approved by the International Mineralogical Association (IMA) under number 2014-051. The type locality (locus typicus) is the Markey Mine in San Juan County, Utah, USA. ## Applications Uroxite has no industrial application. Due to its extreme rarity, microscopic crystal size, and status as a type mineral, it is of interest only to specialized collectors of rare minerals and micromounts.

Properties

Luster
Vitreous to silky
Streak
Light yellow
Density
3.59
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Uroxite can be identified by its intense yellow color, silky luster, and characteristic form of small, acicular or bladed crystals forming radial aggregates. A key feature is its strong fluorescence under ultraviolet light (both short-wave and long-wave) to a bright, greenish-yellow color. It occurs as a secondary mineral in the oxidation zones of uranium deposits. ## Distinguishing from Similar Minerals It can be confused with other yellow secondary uranyl minerals, such as tyuyamunite, carnotite, or meta-autunite. Distinguishing it based on visual features is extremely difficult and most often requires advanced analytical methods, such as X-ray diffraction (XRD) or spectroscopy. Co-occurrence with other uranyl oxalates, like uranoxite, can be a diagnostic indicator. ## Crystal Forms Crystals are very small, bladed or acicular, elongated along the [010] axis. They usually form radial, stellate, or tangled aggregates, as well as thin coatings and efflorescences.

Geological environment

## Genesis Uroxite is a secondary mineral, formed by the weathering (oxidation) processes of primary uranium ores in an environment rich in organic compounds. Its formation is associated with the action of solutions containing oxalic acid, which likely originates from the decomposition of organic matter (e.g., bitumens) present in the host rock (sandstone). ## Mineral Associations This mineral occurs in association with other rare, secondary uranium minerals, particularly other oxalates, such as uranoxite and andersonite. It also co-occurs with gypsum, calcite, pyrite, and clay minerals. ## Localities The only confirmed and described occurrence of uroxite in the world is its type locality – the Markey Mine, Red Canyon, White Canyon District, San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The collector appeal of uroxite specimens primarily depends on the richness and aesthetics of the crystal aggregates. Specimens with clearly formed, radial groups of crystals, densely covering the rock matrix, are most valued. The intensity of the yellow color and contrast with the substrate also influence visual value. Due to its microscopic nature, the quality of a specimen is assessed under magnification. ## Popular Localities The only source of collector specimens is the Markey Mine in Utah, USA. Material from this locality is extremely rare and sought after by collectors specializing in systematics, uranium minerals, and micromounts.

Care and storage

## Cleaning Uroxite specimens should be handled with extreme caution. Cleaning is not recommended due to the fragility and small size of the crystals. If absolutely necessary, compressed air (from a safe distance) can be used to remove loose dust. Any contact with water or other liquids should be avoided. ## What to Avoid Contact with water, which can dissolve or damage the crystals, must be strictly avoided. The mineral is sensitive to chemicals, high temperatures, and changes in humidity. It should not be exposed to direct sunlight, which can cause fading. Due to its uranium content, it is radioactive and requires safe handling. ## Storage Uroxite specimens should be stored under stable conditions, in a dry place, away from sources of light and heat. The best solution is a tightly sealed "micromount" container or a perky box, which protects delicate crystals from mechanical damage and dust. It should be stored away from other minerals that may be sensitive to radiation.

External references

Sources

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