Dokuchaevite

Chemical formula: Cu₂+₈O₂(V₅+O₄)₃Cl₃

Dokuchaevite is an extremely rare copper vanadate with chlorine, forming dark green to black crystals in volcanic exhalations.

## Characteristics Dokuchaevite is a mineral from the vanadate group, chemically classified as a copper oxyvanadate with chlorine. It forms very small, tabular or equant crystals, rarely exceeding 0.2 mm. They typically occur as dense clusters, aggregates, and crusts on porous volcanic substrate. Its color ranges from dark green to almost black, and its luster varies from vitreous to submetallic. ## Physical Properties This mineral is opaque, becoming translucent only in very thin fragments, revealing a green color. It is characterized by an uneven fracture and lacks cleavage. Its calculated density is approximately 4.5 g/cm³. Hardness has not been precisely determined. ## Colors and Varieties Dokuchaevite occurs in a uniform dark green to black color. No color varieties or commercial forms are known. ## History and Name The mineral is named in honor of Vasily Vasilyevich Dokuchaev (1846–1903), a prominent Russian geologist and soil scientist, considered the founder of modern soil science. It was officially recognized by the International Mineralogical Association (IMA) in 2012. The type locality and only known occurrence is Tolbachik volcano in Kamchatka. ## Uses Due to its extreme rarity and microscopic crystal size, dokuchaevite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for specialized collectors of rare minerals and microminerals.

Properties

Luster: Vitreous to Sub-Metallic
Streak: Greenish grey
Density: 4.5
Cleavage: None
Fracture: Uneven
Transparency: Opaque, Translucent in thin fragments
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of dokuchaevite is primarily based on its unique origin – it is a product of volcanic sublimation from a specific fumarole on Tolbachik volcano. Visual characteristics include a dark green to black color, formation of crusts, and small, tabular crystals. Definitive identification is almost exclusively possible based on chemical analysis (EDS) and structural analysis (XRD). ## Distinguishing from Similar Minerals It can be confused with other dark copper minerals found in the same environment, such as tenorite, belloite, or other rare vanadates. Distinguishing it from these with the naked eye is practically impossible and requires advanced analytical methods. ## Crystal Forms Crystals are most often tabular, with a pseudohexagonal or rhombic habit, as well as equant. They usually form dense, rosette-like aggregates, crusts, or fill small voids in the rock.

Geological environment

## Genesis Dokuchaevite is a secondary mineral, formed as a result of exhalative processes. It crystallizes directly from hot volcanic gases (sublimate) in active fumarole zones. This process occurs at relatively high temperatures, estimated at 250-350°C. ## Mineral Associations This mineral occurs in association with other rare fumarole products of Tolbachik volcano. The most common associations include belloite, avdoninite, anhydrokainite, atacamite, as well as hematite and tenorite. ## Localities The only confirmed occurrence of dokuchaevite in the world is its type locality: Yadovitaya fumarole on the Second Northern Breakout Cone of the Great Fissure Eruption of Tolbachik volcano on the Kamchatka Peninsula, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of collectible dokuchaevite specimens is assessed primarily through the lens of micromineralogy. Specimens with well-formed, sharp crystals, even if microscopic in size, are most highly valued. The abundance of the mineral on the rock matrix and the presence of interesting associated minerals that confirm its origin are also important. ## Popular Localities The only source of dokuchaevite specimens is Tolbachik volcano in Kamchatka. Specimens from this locality are highly prized by collectors specializing in minerals from specific localities (so-called "locality collectors") and in rare mineral species.

Care and storage

## Cleaning Dokuchaevite specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Any contact with water and other liquids should be avoided. ## What to Avoid As a mineral formed in fumarolic processes and containing chlorine, dokuchaevite is potentially sensitive to moisture, which can lead to its slow decomposition. Ultrasonic cleaners, all chemical agents, acids, and sudden temperature changes must be strictly avoided. ## Storage It is recommended to store specimens in a dry environment, preferably in a sealed container (e.g., a micromount box) with a desiccant (silica gel). It should be protected from direct sunlight and dust.

Sources

IMA Mineral List (CNMNC)