Avdoninite

Chemical formula: K₂Cu₂+₅Cl₈(OH)₄·₂H₂O

Avdoninite is an extremely rare copper mineral, forming emerald-green, tabular crystals in volcanic exhalation products.

## Characteristics Avdoninite is a hydrated potassium copper hydroxychloride with the formula K₂Cu₅Cl₈(OH)₄·2H₂O. It forms very small, thin, tabular or platy crystals, rarely exceeding 1 mm. They typically occur as radial or chaotic aggregates, as well as thin crusts and coatings on basaltic lava. Its most distinctive feature is a vivid, emerald-green to dark-green color. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of about 3. It has a vitreous luster and is transparent to translucent. The calculated density is 3.19 g/cm³. It is a brittle mineral, exhibiting perfect cleavage in one plane, which corresponds to its tabular habit. ## Colors and Varieties Avdoninite occurs in a uniform, emerald-green color, which may be slightly darker in thicker aggregates. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral was first described in 2014 by a team of mineralogists led by Igor V. Pekov. The name honors Vladimir Nikolaevich Avdonin (1927-2011), a Russian mineralogist and professor at the Ural State Mining University, known for his research on Ural deposits. The type locality is the fumaroles of the Great Fissure Eruption of Tolbachik volcano in Kamchatka, Russia.

Properties

Mohs hardness: 3
Luster: Vitreous
Streak: Pale green
Density: 3.19
Cleavage: Perfect on {001}
Transparency: Transparent to Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of avdoninite include its emerald-green color, thin-tabular crystal habit, vitreous luster, and specific occurrence environment – volcanic fumaroles. It is a hygroscopic mineral, which can also be an indicator. ## Distinguishing from Similar Minerals It can be confused with other green secondary copper minerals, such as belloite, eriochalcite, atacamite, or paratacamite. Distinguishing it from these minerals based on visual characteristics is very difficult and usually requires advanced analytical methods, such as X-ray diffraction (XRD). Key for preliminary identification are the crystal habit (thin plates) and mineral paragenesis. ## Crystal Forms Crystals are thin-tabular, platy, or bladed. They usually form fan-shaped, radial, or irregular aggregates, as well as thin coatings and efflorescences.

Geological environment

## Genesis Avdoninite is a mineral of volcanic origin, formed by exhalation (sublimation from hot volcanic gases). It crystallizes in active fumarole zones, at temperatures above 150°C, as a result of gas reactions with copper-rich basaltic lava. ## Mineral Associations It most often co-occurs with other rare fumarolic minerals, such as belloite, eriochalcite, sylvite, halite, and carnallite. Hematite and tenorite are also associated with it. ## Localities It is an extremely rare mineral, known almost exclusively from its type locality – fumaroles formed during the Great Fissure Eruption of Tolbachik volcano (1975-1976) and the Arsenatnaya and Glavnaya Tenoritovaya fumaroles on the second cone of the same volcano in Kamchatka, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of collector specimens, which are almost exclusively micromounts, is assessed based on several criteria. Samples with well-formed, sharp, and clearly separated crystals of intense emerald color are most highly valued. The abundance of the mineral on the rock matrix and an attractive composition with other rare associated minerals are also important. ## Popular Localities The only source of avdoninite collector specimens is the Tolbachik volcanic complex in Kamchatka, Russia. Specimens from the historic eruption of 1975-1976 and from more recent fumarolic activities are most sought after by specialized collectors.

Care and storage

## Cleaning Avdoninite is an extremely sensitive mineral and requires exceptional care. Wet cleaning is absolutely forbidden, as the mineral is water-soluble and hygroscopic. Dust can be removed very carefully using a soft, dry brush or a gentle puff of compressed air from a distance. ## What to Avoid Contact with water, water vapor, and high humidity must be strictly avoided, as these can lead to its decomposition. Exposure to chemicals, ultrasound, sudden temperature changes, and mechanical shocks is also inadvisable due to its brittleness and perfect cleavage. ## Storage Avdoninite specimens must be stored in sealed, airtight containers (e.g., "perky boxes") away from sources of moisture. It is recommended to place a desiccant (e.g., silica gel) in the container to ensure low humidity. It should be protected from direct sunlight and dust.

Sources

IMA Mineral List (CNMNC)