Pokhodyashinite

Chemical formula: Cu₁+Tl₁+Sb₃+₂(Sb₃+₀.₇Tl₁+₀.₃)As₃+S₂-₆.₇

Pokhodyashinit is an extremely rare thallium, copper, antimony, and arsenic sulfosalt, forming acicular crystals with a metallic luster.

## Characteristics Pokhodyashinit is a very rare mineral from the sulfosalt group, composed of copper, thallium, antimony, arsenic, and sulfur. It forms small, prismatic or acicular crystals, rarely exceeding 0.5 mm in length. These crystals often occur as radial or fan-shaped aggregates. The mineral is black and completely opaque. ## Physical Properties It is characterized by a strong, metallic luster. Its density, calculated based on chemical composition and unit cell parameters, is 5.23 g/cm³. The hardness of the mineral has not yet been determined. It is brittle. ## Colors and Varieties Pokhodyashinit occurs exclusively in black. No color varieties or commercial varieties are known. ## History and Name The mineral was approved by the IMA in 2004. Its name commemorates Nikolai Dmitrievich Pokhodyashin (1950–2010), a Russian mineralogist and specialist in the mineralogy of Ural ore deposits. It was described based on material collected from its only known occurrence. ## Uses Due to its extreme rarity, small crystal size, and toxic chemical composition (thallium and arsenic content), pokhodyashinit has no practical applications. It is solely an object of scientific and collecting interest for specialized micromineral collectors.

Properties

Luster: Metallic
Streak: Black
Density: 5.23
Cleavage: None
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identifying pokhodyashinit under amateur conditions is practically impossible. Indicative features may include its black color, metallic luster, and the form of small, acicular crystals in radial aggregates. Its occurrence in association with other rare arsenic-thallium minerals at the only known locality is crucial. Definitive identification requires advanced analytical methods, such as EDS/WDS analysis or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with many other black, metallic sulfosalts, such as stibnite, which, however, forms much larger crystals. Distinguishing it from co-occurring minerals such as aktashite, galkhaite, or wakabayashilite is impossible without specialized research equipment. ## Crystal Forms It forms elongated, prismatic to acicular crystals, typically up to 0.5 mm long. These crystals arrange themselves into characteristic radial or fan-shaped aggregates.

Geological environment

## Genesis Pokhodyashinit is a hydrothermal mineral. It forms under low-temperature conditions within arsenic-antimony-sulfosalt mineralization, which develops in metasomatized rocks (berezytes) at the contact with limestones. ## Mineral Associations It co-occurs with other rare thallium and arsenic-bearing minerals, such as aktashite, galkhaite, and wakabayashilite. It is also accompanied by realgar, orpiment, stibnite, pyrite, sphalerite, as well as native gold and native arsenic. ## Localities The only confirmed locality for pokhodyashinit in the world is the Vorontsovskoe gold deposit, located in the Serov district of the Sverdlovsk Oblast in the Urals, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a micromineral, specimens with well-formed, sharp, and undamaged crystals, even if sub-millimeter in size, are most highly valued. The value of a specimen is enhanced by the abundance of pokhodyashinit on the rock matrix and its association with other well-crystallized, rare minerals. ## Popular Localities Specimens originate exclusively from the type locality – the Vorontsovskoe gold deposit in Russia. Material from this location is extremely difficult to obtain.

Care and storage

## Cleaning Pokhodyashinit specimens are extremely delicate and small, so they should not be cleaned mechanically or with liquids. The only safe method for dust removal is using compressed air from a safe distance. ## What to Avoid The mineral contains thallium and arsenic, which are highly toxic elements. Inhaling dust and direct skin contact must be strictly avoided. Hands should be thoroughly washed after any contact with the specimen. The mineral should be protected from moisture, high temperatures, and chemicals. ## Storage It is recommended to store specimens in tightly sealed, transparent containers (e.g., micromount type) that protect against dusting and accidental contact. Each container should be clearly labeled as toxic material.

Sources

IMA Mineral List (CNMNC)