Vasilseverginite

Chemical formula: Cu²⁺₉O₄(As⁵⁺O₄)₂(S⁶⁺O₄)₂

Vasilseverginite is a very rare copper arsenate-sulfate, forming microscopic, tabular crystals of an intense green color.

## Characteristics Vasilseverginite is a complex copper arsenate-sulfate, occurring as very fine, tabular or bladed crystals, rarely exceeding 0.2 mm in length. It forms rosette-like or radial aggregates, as well as thin coatings and crusts. Its most characteristic feature is its intense, emerald-green to dark-green color. ## Physical Properties Crystals exhibit a vitreous luster. Due to the microscopic size of the crystals, many physical properties, such as hardness or density, have not been precisely determined. The density calculated based on the formula and unit cell parameters is 4.51 g/cm³. ## Colors and Varieties This mineral occurs in shades from emerald-green to dark-green. No varieties have been distinguished. ## History and Name The mineral's name honors Vasily Mikhailovich Severgin (1765-1826), a Russian chemist and mineralogist, member of the Russian Academy of Sciences. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2011. The discovery was made on archival material from Tolbachik volcano in Kamchatka. ## Applications Vasilseverginite has no industrial application. It is of purely scientific and collector's interest as a very rare mineral.

Properties

Mohs hardness: 3
Color: Bright green
Luster: Vitreous
Streak: Light green
Density: 4.409
Cleavage: Perfect on {100}
Fracture: Irregular/Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of vasilseverginite is based on its characteristic, intense green color, specific form of microscopic, tabular crystals forming rosette-like aggregates, and its origin. Certain identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS). ## Distinguishing from similar minerals It can be confused with other secondary green copper minerals, such as brochantite, linarite, malachite, or euchroite. Differentiation with the naked eye is practically impossible. Vasilseverginite is distinguished by its unique chemical composition (it is both an arsenate and a sulfate) and specific crystal habit, visible under high magnification. ## Crystal forms It forms very small, thin, tabular crystals, often with a hexagonal or rhombic outline. These crystals group into radial or rosette-like aggregates, and also form thin crusts and coatings on the host rock.

Geological environment

## Genesis Vasilseverginite is a fumarolic mineral. It forms as a result of volcanic exhalations, where hot gases rich in copper, arsenic, and sulfur react with volcanic rocks in an oxygen-rich environment. It crystallizes in zones with temperatures around 100-150°C. ## Mineral associations It coexists with other rare fumarolic minerals, such as tenorite, hematite, aphthitalite, langbeinite, anorthite, lammerite, eriostevensite, popovite, urusovite, arsmirandite, and johillerite. ## Localities The only confirmed occurrence of this mineral in the world is its type locality – the Arsenatnaya fumarole field on the second cinder cone of the northern breach of the Great Fissure Eruption of Tolbachik (1975-1976) on Tolbachik volcano, Kamchatka, Russia.

Rarity

Very rare

For collectors

## Quality criteria The quality of vasilseverginite specimens is assessed primarily based on the richness and aesthetics of the crystalline aggregates. Most valued are specimens with clearly formed, rosette-like clusters of an intense, emerald-green color, contrasting with a lighter host rock. Due to the microscopic nature of the mineral, the quality of the photograph taken under a microscope (so-called photomicrography) is crucial. ## Popular localities All known collector specimens come from a single location in the world – Tolbachik volcano in Kamchatka, Russia. Material from this locality is extremely rare and sought after by collectors specializing in systematic minerals and micromounts.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to extreme delicacy and reactivity, any contact with water, chemical solutions, or even a damp cloth should be avoided. ## What to avoid Contact with water and acids, which can damage or dissolve it, must be strictly avoided. The mineral is sensitive to changes in temperature and humidity. It should not be heated or exposed to direct sunlight. ## Storage Vasilseverginite specimens should be stored in airtight, sealed containers (e.g., "micromount boxes") away from dust, moisture, and heat sources. It is best to store them under stable room conditions.