Elasmochloite

Chemical formula: Na₃Cu₂+₆Bi₃+O₄(S₆+O₄)₅

Elasmochloite is a very rare copper, sodium, and bismuth sulfate, discovered in the sublimation products of the Tolbachik volcano in Russia.

## Characteristics Elasmochloite is a sulfate mineral that forms under specific volcanic conditions. Its name comes from the Greek words *elasmos* (plate, lamella) and *chloos* (green), referring to its typical appearance – thin, platy crystals of an intensely green color. These crystals are usually very small, reaching sizes up to 0.2 x 0.1 x 0.01 mm, and often form aggregates or thin coatings on the surface of volcanic rock. ## Physical Properties Elasmochloite crystals are very brittle and exhibit a vitreous luster. Due to their small size and rarity, many of its physical properties, such as density, have not been precisely measured, but rather calculated based on crystallographic data. ## Colors and Varieties This mineral is characterized by a vivid, green color. No color varieties or commercial varieties are known. ## History and Name Elasmochloite was first described by a team of mineralogists led by Igor V. Pekov. Its discovery was approved by the International Mineralogical Association (IMA) in 2015 under number 2015-058. The name, as mentioned, directly refers to its appearance – green, platy crystals.

Properties

Mohs hardness: 2.5
Luster: Vitreous
Streak: Green
Density: 4.33
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of elasmochloite is primarily based on its characteristic appearance – thin, tabular crystals of an intensely green color. The occurrence locality – volcanic fumaroles – is also key. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS). ## Distinguishing from Similar Minerals Elasmochloite can be confused with other green secondary copper minerals, such as brochantite, malachite, or euchlorine, which also occur in volcanic environments. Distinguishing it with the naked eye is practically impossible. It is distinguished by its unique, platy crystal form and specific chemical composition (presence of bismuth and sodium). ## Crystal Forms This mineral forms very thin, tabular or platy crystals, often flattened. They usually occur as small aggregates, clusters, or as single, dispersed crystals on the substrate.

Geological environment

## Genesis Elasmochloite is a mineral of volcanic origin. It forms as a result of exhalative processes, crystallizing directly from volcanic gases (sublimation) at a temperature of approximately 450°C. It forms in the vicinity of active fumaroles, where hot gases rich in sulfur, copper, sodium, and bismuth react with atmospheric oxygen. ## Mineral Associations This mineral occurs in association with other rare fumarolic minerals, such as tenorite, hematite, magnesium-langbeinite, arcanite, euchlorine, eriocalcite, chalcocyanite, alexandrowite, and urusovite. ## Localities The only confirmed locality of elasmochloite in the world is its type locality – Arsenatnaya fumarole field, located on the second cinder cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption on Tolbachik volcano (Kamchatka, Russia).

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, the quality of a specimen is primarily determined by the abundance and development of crystals on the rock matrix. Specimens with numerous, well-defined, intensely green lamellae forming aesthetic aggregates are most valued. Association with other rare minerals from this locality is also important. ## Popular Localities The only source of elasmochloite specimens is its discovery site on the Tolbachik volcano in Kamchatka. All specimens available on the collector's market come from this single, specific locality.

Care and storage

## Cleaning Due to the extreme brittleness and small size of the crystals, mechanical cleaning is not recommended. Specimens should be protected from dust by storing them in sealed containers. If cleaning is absolutely necessary, compressed air can be used from a very long distance and at minimal pressure. ## What to Avoid Contact with water and any chemicals should be avoided, as being a sulfate formed by sublimation, it may be soluble. Vibrations, shocks, and any touch that could damage the delicate crystals should also be avoided. ## Storage Elasmochloite specimens should be stored exclusively in specialized, sealed "micromount" boxes, which protect them from mechanical damage, dust, and moisture. Display should be away from sources of vibration and direct sunlight.

Sources

IMA Mineral List (CNMNC)