Ilinskite

Chemical formula: NaCu<sup>2+</sup><sub>5</sub>O<sub>2</sub>(Se<sup>4+</sup>O<sub>3</sub>)<sub>2</sub>Cl<sub>3</sub>

Ilinskite is a very rare copper and sodium selenite, forming microscopic, tabular crystals of an intense green color.

## Characteristics Ilinskite is a mineral from the selenite group, occurring as very fine, tabular or bladed crystals, rarely exceeding 0.2 mm in length. These crystals form scattered clusters or rosette-like aggregates on the surface of the host rock. Due to their size, visual features are mainly discernible under a microscope. The mineral is characterized by an intense, emerald-green color. ## Physical Properties Ilinskite crystals exhibit a vitreous luster. They are transparent to translucent. Due to the small size of the crystals, determining hardness and density is difficult; the density calculated based on the chemical formula and unit cell parameters is 4.11 g/cm³. ## Colors and Varieties Ilinskite occurs in one characteristic color – emerald-green. No color varieties or commercial varieties are known. ## History and Name The mineral's name honors Georgy Alekseevich Ilinsky (1927–1999), a Russian mineralogist and crystallographer from St. Petersburg University. Ilinskite was discovered in fumarolic products of the Tolbachik volcano in Kamchatka, Russia, and approved as a new mineral species by the International Mineralogical Association (IMA) in 1996. ## Uses Ilinskite has no practical applications. Its significance is purely scientific and as a collector's item, being a unique and rare mineral.

Properties

Luster
Vitreous
Streak
Green
Density
4.11
Cleavage
Perfect on {100}
Transparency
Transparent to Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of ilinskite is based on its unique occurrence environment (volcanic fumaroles), characteristic emerald-green color, tabular form of microscopic crystals, and co-occurrence with other rare selenites. Definitive identification requires advanced analytical techniques such as X-ray diffraction (XRD) or energy-dispersive spectroscopy (EDS). ## Distinguishing from Similar Minerals Ilinskite can be confused with other green secondary minerals found in the same environment, such as sophiite, georgbokiite, or chloromenite. Distinguishing it "by eye" is practically impossible. Key differences lie in the chemical composition (presence of sodium and chlorine in ilinskite) and crystal structure, which requires laboratory confirmation. ## Crystal Forms Ilinskite forms thin, tabular or bladed crystals, often flattened. They occur as single, scattered plates or form small, radial aggregates resembling rosettes.

Geological environment

## Genesis Ilinskite is a mineral of volcanic origin, formed by sublimation in high-temperature (400-600°C) exhalations (fumaroles). It crystallizes directly from volcanic gases rich in selenium, copper, sodium, and chlorine, depositing on porous basalt. ## Mineral Associations This mineral occurs in association with other rare selenites and chlorides, such as sophiite, georgbokiite, chloromenite, halite, sylvite, hematite, and tenorite. Co-occurrence with these minerals is a key diagnostic indicator. ## Localities The only confirmed locality for ilinskite worldwide is its type locality: the products of fumarolic activity of the Great Fissure eruption of Tolbachik volcano on the Kamchatka Peninsula, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an ilinskite specimen primarily depends on the abundance and visibility of crystals on the rock matrix. Samples with numerous, well-formed, intensely green crystals forming aesthetic clusters are most valued. Crystal size, even if microscopic, is also important – larger plates are more desirable. Contrast with a light host rock enhances visual appeal. ## Popular Localities The only source of ilinskite specimens is the Tolbachik volcano in Kamchatka. Material from historical eruptions and fumarolic activity is extremely limited, making each specimen unique.

Care and storage

## Cleaning Due to the extreme rarity and fragility of specimens, mechanical or chemical cleaning is not recommended. Any contaminants should be left undisturbed. If absolutely necessary, a gentle stream of compressed air can be used from a distance. ## What to Avoid Avoid contact with water, acids, cleaning agents, and ultrasound. The mineral is sensitive to changes in temperature and humidity. It should be protected from direct sunlight, which can cause fading. ## Storage Ilinskite specimens should be stored exclusively in specialized, sealed "micromount" containers, protecting them from dust, moisture, and mechanical damage. Display should occur under stable environmental conditions.

Sources

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