Polekhovskyite

Chemical formula: MoNiP₂

Polekhovskyite is an extremely rare molybdenum and nickel phosphide, discovered in a meteorite and known only from a single microscopic grain.

## Characteristics Polekhovskyite is a mineral known to science exclusively from a single, microscopic grain (approx. 4x7 μm), which was found as an inclusion in another rare mineral, allabogdanite. This grain has an irregular, xenomorphic shape and is opaque, with a metallic luster and a gray color in reflected light. Due to its extreme rarity and microscopic size, most of its physical properties remain unknown or have been estimated based on chemical and structural analysis. ## Physical Properties Due to the size of the only known grain, it was not possible to directly measure properties such as hardness, density, cleavage, or fracture. Density was calculated based on chemical composition and unit cell parameters and is 7.21 g/cm³. The mineral exhibits a metallic luster. ## History and Name The mineral is named in honor of Ukrainian mineralogist and collector Yuriy Polekhovsky (born 1958), in recognition of his contribution to the study of minerals in Ukraine. Polekhovskyite was officially approved by the International Mineralogical Association (IMA) in 2020 (IMA2020-050). The discovery was made in a sample from the heavily shocked Onello iron meteorite, found in 1998 in the Onello River basin in Yakutia, Russia.

Properties

Color
Bluish-gray
Luster
Metallic
Density
6.626
Transparency
Opaque
Crystal system
Hexagonal

Diagnostic features

## Identification Identification of polekhovskyite is possible only using advanced laboratory techniques, such as scanning electron microscopy (SEM) combined with chemical composition analysis (EDS/WDS) and electron backscatter diffraction (EBSD) to determine the crystal structure. In reflected light, it is gray and opaque. ## Differentiation from Similar Minerals This mineral occurs in paragenesis with other rare meteoritic phosphides, such as allabogdanite, nickelphosphide, and schreibersite. Differentiation from these requires precise analysis of the molybdenum to nickel and phosphorus ratio and confirmation of its hexagonal crystal structure, which distinguishes it from monoclinic allabogdanite.

Geological environment

## Genesis Polekhovskyite formed under extreme pressure and temperature conditions that occurred during a high-energy impact in outer space, leading to the formation of the Onello meteorite's parent body. It is a product of shock metamorphism that acted on pre-existing minerals, likely phosphides such as schreibersite, in the presence of molybdenum. ## Mineral Associations This mineral was found as an inclusion in allabogdanite. It co-occurs with other minerals typical of heavily shocked iron meteorites, such as taenite, plessite, graphite, schreibersite, nickelphosphide, and high-pressure silica polymorphs. ## Localities The only confirmed locality for polekhovskyite in the world is the Onello iron meteorite (IAB-MG group), found in the Onello River basin, in the Sakha Republic (Yakutia), Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria Polekhovskyite is not a mineral available on the collector's market. Its value is purely scientific. The only known material (type material) is stored in the collection of the A.E. Fersman Mineralogical Museum in Moscow. Theoretically, any verified fragment of the Onello meteorite containing this mineral would be an object of immense scientific and potentially material value, but finding another grain is highly improbable.

Care and storage

## Cleaning Due to its microscopic size and occurrence as an inclusion, polekhovskyite specimens are not subject to cleaning in the traditional sense. Any research preparations (polished sections) require specialized laboratory techniques. ## What to Avoid As a mineral found in iron meteorites, it is potentially susceptible to moisture and oxidation under terrestrial conditions. Contact with water, chemicals, and humid air, which could lead to its decomposition, should be avoided. ## Storage The only known samples are stored under controlled conditions in scientific institutions, most often in desiccators or an inert gas atmosphere, to prevent degradation. The type material is stored at the A.E. Fersman Mineralogical Museum in Moscow.

External references

Sources

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