Meniaylovite

Chemical formula: Ca<sub>4</sub>AlSi(S<sup>6+</sup>O<sub>4</sub>)F<sub>13</sub>·12H<sub>2</sub>O

Meniaylovite is an extremely rare calcium aluminum sulfatofluorosilicate, forming colorless, acicular crystals in products of volcanic activity.

## Characteristics Meniaylovite is a complex hydrated calcium aluminum sulfatofluorosilicate. It occurs as very fine, acicular or hair-like crystals, which typically form small, radial aggregates or tangled masses resembling glass wool. Individual crystals are colorless and transparent, and their small size makes the aggregates appear white with a silky luster. ## Physical Properties Meniaylovite crystals are extremely small and fragile. Due to their mode of occurrence, precise determination of many physical properties, such as hardness or density, is impossible or has not yet been carried out. The luster of the aggregates is described as silky. ## History and Name The mineral was named in honor of Igor Aleksandrovich Meniaylov (1937-1993), a Russian volcanologist from the Institute of Volcanology in Petropavlovsk-Kamchatsky. Meniaylov was a pioneer in the study of volcanic gases and tragically died during the eruption of Galeras volcano in Colombia. The mineral was approved by the IMA in 2019. ## Uses Meniaylovite has no practical applications. It is of interest solely for scientific and collecting purposes due to its extreme rarity and specific formation environment.

Properties

Luster
Silky
Streak
White
Transparency
Transparent to translucent
Crystal system
Tetragonal

Diagnostic features

## Identification Identification of meniaylovite is primarily based on its unique appearance – fine, acicular crystals forming radial or tangled aggregates. Key factors include its occurrence (volcanic exhalation products) and association with other rare fumarolic minerals. Identification requires advanced analytical methods such as XRD and EDS. ## Distinguishing from Similar Minerals It can be confused with other white, acicular fumarolic minerals, such as ralstonite or gearksutite. Differentiation in the field is practically impossible and requires laboratory analysis. The characteristic radial habit of the aggregates can be a clue. ## Crystal Forms It forms elongated, acicular or hair-like crystals up to 0.5 mm long and only a few micrometers thick. These crystals combine into radial aggregates up to 1 mm in diameter or form tangled, woolly masses.

Geological environment

## Genesis Meniaylovite is a fumarolic mineral. It forms by direct sublimation from volcanic gases rich in fluorine, sulfur, and silica, at temperatures of approximately 100-120°C. It crystallizes on the surface of volcanic rocks near active fumaroles. ## Mineral Associations It co-occurs with other fumarolic minerals, such as ralstonite, gearksutite, yaroslavite, as well as opal and alunogen. These minerals form complex, multiphase coatings and crusts. ## Localities The only known locality for meniaylovite in the world (type locality) is the fumarole field on the northern slope of the Nabokoite cone, formed during the Great Tolbachik Fissure Eruption in 2012-2013 on Kamchatka, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria For collectors, the size and quality of the aggregates are most important. Specimens with clearly formed, radial "sunbursts" of acicular crystals, contrasting with the dark host rock, are most prized. Due to its extreme rarity, any well-formed and undamaged specimen is valuable. ## Popular Localities All known specimens come exclusively from one location in the world – Tolbachik volcano on Kamchatka, Russia. Material from this locality is extremely limited and rarely appears on the market.

Care and storage

## Cleaning Meniaylovite specimens should not be cleaned mechanically or chemically. The fine, acicular crystals are extremely fragile and easily damaged. Any attempt at cleaning risks irreversible damage to the specimen. ## What to Avoid Contact with water and chemicals must be strictly avoided, as the mineral is water-soluble. It should be protected from moisture, temperature changes, and any vibrations or impacts. ## Storage Specimens should be stored under stable conditions, in a tightly sealed, transparent "micromount" container, which will protect them from moisture, dust, and mechanical damage. Do not expose it to direct sunlight.

Sources

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