Alumoedtollite

Chemical formula: K₂NaCu₂+₅AlO₂(As₅+O₄)₄

An extremely rare copper, sodium, potassium, and aluminum arsenate, forming microscopic, dark green crystals in volcanic fumaroles.

## Characteristics Alumoedtollite is a complex arsenate that visually appears as very small, prismatic crystals of a dark green, greenish-black, or almost black color. It typically forms small, radial aggregates, crusts, or occurs as individual, imperfectly formed crystals. Due to its microscopic size, its features are difficult to observe without magnification. The luster is described as vitreous. ## Physical Properties Alumoedtollite crystals are brittle. This mineral is translucent in thin fragments, but becomes opaque in larger masses. Its density, calculated from the chemical formula and unit cell parameters, is approximately 4.45 g/cm³. Hardness has not been precisely determined. ## Colors and Varieties This mineral occurs in a uniform, dark color range, from dark green to black. No color or commercial varieties have been distinguished. ## History and Name The name alumoedtollite refers to its chemical composition – it is an aluminum (Al) analog of edtollite, in which aluminum replaces iron. The mineral was officially approved by the International Mineralogical Association (IMA) in 2017. Its discovery was made in the Arsenatnaya fumarole on the Tolbachik volcano (Kamchatka, Russia), which is the only known locality for its occurrence. ## Applications Alumoedtollite, as an extremely rare mineral occurring in microscopic quantities, has no practical application. It is solely an object of scientific research and is valued in specialized systematic collections.

Properties

Luster: Vitreous
Streak: Grayish-green
Density: 4.45
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of alumoedtollite is impossible without advanced analytical techniques. Due to its microscopic size and occurrence in complex parageneses, it requires analysis of chemical composition (EDS/WDS) and crystal structure (XRD). Visual features, such as dark green color and radial aggregates, are only an indication and do not allow for certain identification. ## Distinguishing from Similar Minerals Alumoedtollite is visually indistinguishable from many other rare copper arsenates found in the fumaroles of Tolbachik volcano, such as edtollite (its iron analog), arsmirandite, lehmannite, or lammerite. Certain differentiation is possible only on the basis of chemical analysis, which will show the presence of aluminum in the mineral's structure. ## Crystal Forms Alumoedtollite forms short, prismatic crystals that often intergrow into radial or chaotic aggregates. It also occurs as thin crusts on volcanic rocks.

Geological environment

## Genesis Alumoedtollite is a fumarolic mineral. It forms as a result of sublimation from hot volcanic gases, rich in arsenic, copper, and other metals, in an environment of high oxygen activity. It crystallizes directly on the walls of fumarole channels at a temperature of approximately 450-500°C. ## Mineral Associations This mineral occurs in association with other volcanic sublimates. Its most common associations include: tenorite, hematite, sanidine, aphthitalite, langbeinite, as well as rarer arsenates such as lammerite, urusovite, arsmirandite, lehmannite, and johillerite. ## Localities The only confirmed and described locality of alumoedtollite in the world is its type locality – the Arsenatnaya fumarole, located on the second cinder cone of the northern breach of the Great Fissure Eruption of Tolbachik volcano on the Kamchatka Peninsula in Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, specimens with well-formed, sharp crystals, preferably forming aesthetic, radial aggregates, are most highly valued. A contrasting rock matrix enhances the attractiveness of the specimen. The abundance of the mineral on the sample surface is also important. However, the key element of value is certainty of identification, confirmed by the discoverer or a laboratory. ## Popular Localities The only source of alumoedtollite specimens is its type locality on the Tolbachik volcano in Kamchatka. Material from this location is extremely rare and available almost exclusively in specialized circulation.

Care and storage

## Cleaning Alumoedtollite specimens are extremely delicate and sensitive. Cleaning should be limited to an absolute minimum. Only very careful dust removal with a soft brush or a stream of compressed air from a safe distance is permissible. Any contact with water and chemical agents should be avoided. ## What to Avoid Alumoedtollite is an arsenate, which means it is toxic – ingestion and inhalation of dust should be avoided. Hands should be thoroughly washed after any contact with the specimen. The mineral is likely sensitive to moisture and temperature changes. Ultrasonic cleaners or any solvents must not be used. ## Storage Specimens should be stored in stable conditions, in a closed, dry "micromount" container, protecting them from dust, moisture, and direct light exposure. Due to its brittleness, vibrations and shocks should be avoided.

Sources

IMA Mineral List (CNMNC)