Polkanovite

Chemical formula: Rh<sub>₁₂</sub>As<sub>₇</sub>

Polkanovite is a very rare rhodium arsenide, forming metallic, hexagonal crystals and flakes of a tin-white color.

## Characteristics Polkanovite is a rhodium arsenide, belonging to very rare minerals. It occurs as small, hexagonal plates and flakes, less frequently as inclusions in other minerals. Its typical specimens do not exceed 0.2 mm in size. It is characterized by a metallic luster and a tin-white color, often with a gray tint. It is an opaque mineral. ## Physical properties Due to the small size of the crystals, many physical properties of polkanovite have not been precisely determined. Hardness on the Mohs scale is estimated at about 5. This mineral is brittle and has a relatively high density of 11.27 g/cm³, which is characteristic of minerals containing platinum-group metals. ## Colors and varieties Polkanovite has a constant, tin-white color, appearing grayish in reflected light. No color varieties or commercial varieties are known. ## History and name The mineral was discovered in the Miassitovoye deposit in the Guli (or Gulinsky) massif in Siberia, Russia. It was approved by the International Mineralogical Association (IMA) in 1997. The name honors Yuri Alexandrovich Polkanov (1935-2020), a Ukrainian mineralogist and geologist, researcher of platinum-group minerals in Ukraine. ## Applications Polkanovite has no industrial application. Its significance is purely scientific and collectible, as a unique and rare representative of platinum-group metal arsenides.

Properties

Mohs hardness: 5
Luster: Metallic
Streak: Grayish-black
Density: 11.27
Cleavage: Perfect on {0001}
Fracture: Brittle
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of polkanovite under amateur conditions is practically impossible. It requires advanced laboratory methods, such as chemical composition analysis (EDS/WDS) using an electron microprobe and X-ray diffraction (XRD) analysis to confirm the crystal structure. In reflected light under a polarizing microscope, it shows weak anisotropy. ## Differentiation from similar minerals It can be confused with other rare platinum-group metal arsenides, such as palladoarsenide, majakite, or sperrylite, as well as native rhodium. Definitive differentiation is possible only through detailed chemical and structural analyses. ## Crystal forms Polkanovite forms very small, hexagonal crystals with a tabular or flaky habit. It also occurs as irregular grains and inclusions in other minerals, mainly osbornite and moissanite.

Geological environment

## Genesis Polkanovite forms under specific geological conditions, in ultramafic and alkaline rocks, such as dunites. Its formation is associated with magmatic processes within large layered intrusions rich in platinum-group metals. ## Mineral associations This mineral co-occurs with other rare minerals. In the type locality (Guli massif), it was found in association with osbornite, moissanite, graphite, forsterite, chromite, as well as platinum-group minerals such as ruthenium, iridium, osmium, and rhodium. ## Localities The only confirmed and thoroughly described occurrence of polkanovite in the world is its type locality – the Miassitovoye deposit in the Guli dunite massif on the Putorana Plateau, in the Krasnoyarsk Krai, Siberia, Russia.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of a polkanovite specimen is primarily determined by the possibility of its identification and observation. The most valuable specimens are those with clearly developed, though still microscopic, hexagonal crystals. Rich association with other rare minerals is also important, as it enhances the scientific and collectible value of the sample. ## Popular localities The Guli massif in Siberia is the only source of polkanovite specimens. For this reason, the mineral is practically unavailable on the collector's market and is found almost exclusively in the collections of scientific institutions and museums.

Care and storage

## Cleaning Due to the extreme rarity and small size of specimens, mechanical cleaning is not recommended. Any contaminants should be removed with the utmost care, preferably using compressed air or under laboratory conditions. ## What to avoid Avoid contact with chemicals, especially acids, which can react with arsenides. The mineral should be protected from mechanical damage, abrasion, and high temperatures. ## Storage Polkanovite specimens, typically in the form of microscopic inclusions or flakes, should be stored in specialized, sealed "micromount" boxes, protecting them from dust, moisture, and damage. Display should take place under stable conditions, away from vibrations.

Sources

IMA Mineral List (CNMNC)