Amurselite

Chemical formula: (N<sup>3-</sup>H<sub>4</sub>)<sub>2</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>5</sub>(Se<sup>4+</sup>O<sub>3</sub>)<sub>3</sub>O<sub>2</sub>(OH)<sub>2</sub>(H<sub>2</sub>O)·8H<sub>2</sub>O

Amursite is an extremely rare uranyl mineral, an ammonium selenite, found in the oxidation zones of uranium deposits.

## Characteristics Amursite is a very rare secondary mineral from the uranyl selenite group. It forms microscopic, platy or acicular crystals up to 0.2 mm long, which often occur as radial aggregates or small clusters. Due to its chemical composition, containing uranium, it is a radioactive mineral. ## Physical Properties Amursite crystals exhibit a vitreous luster. It is a relatively soft mineral, with a Mohs hardness of approximately 2. It is transparent to translucent. Density has not been measured, but the calculated value is 4.45 g/cm³. ## Colors and Varieties Amursite is characterized by an intense, yellow-orange color. No varieties are known. ## History and Name The mineral was discovered in the Berezovoye uranium deposit in the Amur River basin in the Amur Oblast, Russian Far East. Its name, approved by the IMA in 2017, comes from the region where its type locality is situated (Amur Oblast). ## Applications Due to its extreme rarity and microscopic crystal size, amursite has no practical applications and is solely an object of scientific interest and a collector's item for specialized collectors of rare minerals.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Light yellow
Density
4.45
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Amursite can be identified by its characteristic yellow-orange color, platy or acicular crystal habit, and occurrence in radial aggregates. A key diagnostic feature is its strong yellow-green fluorescence under ultraviolet light (both shortwave and longwave). Its radioactivity is also an important indicator. ## Distinguishing from Similar Minerals It can be confused with other secondary uranyl minerals of similar color, such as guilleminite or demesmaekerite. Differentiation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD), due to visual similarity and co-occurrence in the same environments. ## Crystal Forms Crystals are very small, usually not exceeding 0.2 mm in length and 0.01 mm in thickness. They have the form of elongated plates or needles, often flattened. They typically form radial or chaotic aggregates.

Geological environment

## Genesis Amursite is a secondary mineral, formed in the oxidation zones of hydrothermal uranium deposits containing selenium. It crystallizes as a result of weathering processes of primary uranium ores (uraninite) in the presence of selenium-rich solutions. ## Mineral Associations This mineral co-occurs with other uranyl selenites, such as guilleminite, demesmaekerite, marthozite, and derriksite. It is also associated with uraninite, hematite, calcite, quartz, and clay minerals. ## Localities The only confirmed locality of amursite in the world is its type locality – the Berezovoye uranium deposit, located in the Amur River basin, in the Amur Oblast, Russian Far East.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of amursite specimens is assessed based on the richness and visibility of clusters on the rock matrix. The most desirable specimens are those with distinct, well-formed, radial aggregates of an intense, yellow-orange color. Due to the microscopic size of the crystals, specimens are evaluated under magnification. ## Popular Localities The only source of amursite specimens is its type locality in Russia, which makes it extremely difficult to acquire on the collector's market.

Care and storage

## Cleaning Amursite specimens should not be cleaned wet. Due to its delicacy and water solubility, the only safe method is to remove dust with a soft brush or compressed air from a safe distance. ## What to Avoid Contact with water, acids, and other chemicals that could damage or dissolve it should be strictly avoided. As a uranyl mineral, it is sensitive to changes in humidity. It should be protected from high temperatures and direct sunlight. ## Storage Amursite is a radioactive mineral and should be stored with appropriate precautions. It is recommended to keep it in a sealed, labeled container, away from other minerals that could be damaged by radiation. Store in a dry place to prevent degradation.

Sources

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