Iriginite

Chemical formula: (U<sup>6+</sup>O<sub>2</sub>)Mo<sup>6+</sup><sub>2</sub>O<sub>7</sub>·3H<sub>2</sub>O

Iriginite is a rare uranyl and molybdenum mineral, forming characteristic, bright yellow coatings and fibrous aggregates.

## Characteristics Iriginite is a hydrated uranyl and molybdenum oxide. It most commonly occurs as earthy, powdery, or dusty coatings and aggregates. It also forms aggregates with a radial-fibrous or spherulitic structure; lamellar aggregates are less common. Its structure and appearance are typical of secondary uranium minerals formed in oxidation zones. ## Physical Properties This mineral is very soft, with a Mohs hardness of 1 to 2. It has a luster described as dull, earthy, and in the case of fibrous aggregates, silky. It is a light mineral, with a density of approximately 4.2 g/cm³. Due to its nature (fine aggregates), it is opaque. ## Colors and Varieties Iriginite is characterized by an intense, bright yellow color, which can transition to canary yellow or pale yellow shades. No distinct color varieties or commercial varieties are recognized. ## History and Name The mineral's name comes from its discovery locality in the Iriginskoye Mountains in the Southern Urals (Russia). It was first described in 1958 by G. A. Sidorenko. ## Uses Due to its rarity and small accumulations, iriginite has no industrial application. It is solely an object of interest for collectors specializing in uranium minerals and for scientific institutions.

Properties

Mohs hardness
1-2
Luster
Dull, Silky
Streak
Pale yellow
Density
4.2
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Opaque
Crystal system
Triclinic

Diagnostic features

## Identification The key diagnostic features of iriginite are its bright, canary-yellow color, low hardness, and occurrence as earthy coatings or delicate fibrous aggregates. Strong radioactivity is also an important indicator. It does not fluoresce under ultraviolet light. ## Distinguishing from Similar Minerals Iriginite can be confused with other yellow secondary uranium minerals, such as carnotite, tyuyamunite, or uranophane. Differentiation often requires chemical analysis (molybdenum test) or X-ray diffraction (XRD) studies. Uranophane often forms more well-developed, acicular crystals, while carnotite and tyuyamunite are typically more granular or powdery. ## Crystal Forms Well-formed crystals are extremely rare. It most commonly forms microcrystalline fibrous, radial, spherulitic aggregates, as well as dusty and earthy coatings on the host rock.

Geological environment

## Genesis Iriginite is a secondary mineral formed in the oxidation (weathering) zones of uranium-molybdenum deposits. It forms as a result of the alteration of primary uranium ores (such as uraninite) and molybdenum (molybdenite) under near-surface conditions, with the involvement of oxygen-rich waters. ## Mineral Associations It often co-occurs with other minerals from the oxidation zone. Typical associated minerals include uraninite, molybdenite (as primary minerals), and gypsum, calcite, jordisite, uranophane, and other secondary molybdates and uranyl minerals. ## Localities The most important localities worldwide, from which well-documented specimens originate, include the Iriginskoye Mountains in the Urals (Russia), the Shinarump uranium deposit (Utah, USA), the Lucky Mc mine (Wyoming, USA), and several localities in Nevada (USA).

Rarity

Rare

For collectors

## Quality Criteria The most prized by collectors are specimens with clearly visible, radial or spherulitic fibrous aggregates of intense, bright yellow color. Contrast with the dark host rock is also important. Specimens in the form of earthy coatings are less attractive, unless they cover a significant surface area. ## Popular Localities Specimens from the classic locality in the Urals and from deposits in Utah, USA, are most sought after by collectors specializing in systematic minerals and uranium minerals.

Care and storage

## Cleaning Iriginite specimens should not be wet cleaned. Due to its fragility and water solubility, the only safe method is to gently remove dust with a soft brush or compressed air from a safe distance. ## What to Avoid Contact with water, acids, and other chemicals that can damage or dissolve it must be strictly avoided. As a uranium mineral, it is radioactive and requires careful handling – avoid inhaling dust and wash hands after each contact. It should not be heated, as it loses structural water. ## Storage Iriginite should be stored in a dry place, in a tightly sealed container (e.g., a "perky box"), to protect it from moisture and mechanical damage. Due to its radioactivity, specimens should be kept away from areas of permanent human habitation and appropriately labeled.

Sources

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