Yaroshevskite

Chemical formula: Cu₂+₉O₂(V₅+O₄)₄Cl₂

Jaroshevskite is a very rare copper vanadate, forming microscopic, tabular crystals of intense black color and metallic luster.

## Characteristics Jaroshevskite is a mineral from the vanadate group, characterized by a complex chemical composition containing copper, vanadium, oxygen, and chlorine. It occurs as very fine, tabular or platy crystals, which rarely exceed 0.2 mm in length. These crystals form aggregates or appear as single flakes on the surface of the host rock. Due to its small size, its macroscopic features are difficult to observe without a microscope. ## Physical Properties Jaroshevskite crystals are black and opaque. They exhibit a strong, metallic luster. Due to the microscopic size of the crystals, hardness and density have not been precisely measured, but only calculated. The calculated density is approximately 4.88 g/cm³. ## Colors and Varieties This mineral is monochromatic – it occurs exclusively in black. It does not form color varieties or commercial forms. ## History and Name Jaroshevskite was discovered on the cinder cones of Tolbachik volcano in Kamchatka, Russia. It was officially recognized by the International Mineralogical Association (IMA) in 2012. Its name honors the Russian geochemist Aleksey Andreevich Yaroshevsky (1928-2013), a professor at Moscow University, for his contributions to the study of magmatic processes and geochemistry. ## Uses Jaroshevskite has no practical or commercial applications. Its significance is purely scientific and collectible, as a unique and rare component of volcanic fumaroles.

Properties

Luster: Metallic
Streak: Black
Density: 4.88
Cleavage: Perfect on {001}
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of jaroshevskite in the field is impossible. In a collection, it is recognized by its characteristic appearance – black, metallic-lustered, tabular crystals on a matrix originating from volcanic fumaroles. Definitive identification requires advanced analytical methods, such as Raman spectroscopy or EDS analysis. ## Distinguishing from Similar Minerals Jaroshevskite can be confused with other black, microcrystalline volcanic minerals, such as tenorite (CuO) or other complex copper vanadates (e.g., piipite). Distinguishing it with the naked eye is practically impossible. Key to identification are its specific occurrence environment (fumaroles) and confirmation of its chemical composition. ## Crystal Forms It forms thin, tabular or platy crystals with a hexagonal outline, often elongated. These crystals occur as single flakes or form small, radial or chaotic aggregates.

Geological environment

## Genesis Jaroshevskite is a mineral of volcanic origin. It forms as a result of exhalative processes, crystallizing from hot gases (fumaroles) rich in copper, vanadium, and chlorine. It sublimes on the surface of volcanic rocks in high-temperature zones. ## Mineral Associations This mineral co-occurs with other rare products of volcanic exhalations. At the type locality (Tolbachik volcano), it was found in association with minerals such as hematite, tenorite, lammerite, leningradite, piipite, urusovite, and popovite. ## Localities The only confirmed locality of jaroshevskite in the world is its type locality – the "Yadovitaya" fumarole on the second cinder cone of the Northern Breakthrough of the Great Fissure Eruption of Tolbachik volcano on the Kamchatka Peninsula, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a jaroshevskite specimen primarily depends on the abundance and visibility of crystals on the matrix. Specimens with numerous, well-formed, lustrous crystals forming dense clusters are most highly valued. Contrast with a lighter host rock also enhances aesthetic value. The size of individual crystals, although always microscopic, is an important factor – the larger they are, the more desirable the specimen. ## Popular Localities The only source of collectible specimens is the type locality – Tolbachik volcano in Kamchatka. Specimens from this location are highly prized by collectors specializing in rare minerals and micromounts.

Care and storage

## Cleaning Jaroshevskite specimens are extremely delicate and sensitive. No mechanical or chemical cleaning is recommended. Dust can only be removed using a gentle puff of air from a photographic blower. ## What to Avoid Contact with water, acids, bases, and all chemical agents must be strictly avoided. The mineral is potentially reactive. It should be protected from moisture, high temperatures, and direct sunlight, which could cause its degradation. ## Storage Specimens should be stored under stable conditions, preferably in closed, airtight "micromount" boxes, away from dust and humidity fluctuations. Due to the fragility and small size of the crystals, all shocks and manipulations should be avoided.

Sources

IMA Mineral List (CNMNC)