Kotulskite

Chemical formula: Pd(Te,Bi)<sub>₂-x</sub> (x ≈ ₀.₄)

Kotulskite is a rare palladium telluride-bismuthide, occurring as microscopic grains with a metallic luster in sulfide deposits.

## Characteristics Kotulskite is a mineral from the sulfide group, although chemically it is a palladium telluride and bismuthide. It usually forms very small, irregular grains that rarely exceed fractions of a millimeter. For this reason, it does not form macroscopic specimens and is mainly studied as polished sections under a microscope. In reflected light, it has a creamy-white color, often with a yellowish or pinkish tint, and is characterized by a high, metallic luster. ## Physical Properties This mineral is opaque. It has a relatively low hardness of 2.5 on the Mohs scale, which means it is quite soft. Its density, however, is very high, approximately 9.3 g/cm³, which is typical for minerals containing heavy metals such as palladium. ## Colors and Varieties Kotulskite has a constant, characteristic creamy-white color, sometimes with a delicate yellowish tint. It does not form color varieties or have commercial names. Its chemical composition may vary slightly in terms of the tellurium to bismuth ratio. ## History and Name The mineral was first described in 1963 by A. D. Genkin, I. V. Murav'eva, and N. N. Znamensky. The name kotulskite was given in honor of Vladimir Klementevich Kotulsky (1879-1951), a Russian geologist and researcher of sulfide ore deposits, including those in the Norilsk region, where this mineral was discovered. ## Applications Kotulskite, as a palladium mineral, is a minor component of ores of this metal. It is not exploited independently, but its presence is of scientific and prospecting significance in the study of platinum-group metal deposits. It is primarily of interest in mineralogical and geological research.

Properties

Mohs hardness: 2.5
Luster: Metallic
Streak: Black
Density: 9.3
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Identification of kotulskite in the field or in a collection without specialized equipment is impossible due to its microscopic size. Under an ore microscope (in reflected light), it is recognized by its creamy-white color with a yellowish tint, strong metallic luster, and high reflectance. Definitive identification requires chemical analysis, most often using an electron microprobe. ## Distinguishing from Similar Minerals Kotulskite is extremely difficult to distinguish from other bright tellurides and bismuthides of platinum-group metals, such as merenskyite, moncheite, sobolevskite, or froodite. All these minerals have a similar appearance and occur in the same parageneses. Differentiation is based solely on precise chemical composition analysis. ## Crystal Forms Kotulskite most often occurs as anhedral (irregular) grains. Sometimes it forms small aggregates with a granular or bladed texture, often intergrown with other platinum-group minerals.

Geological environment

## Genesis Kotulskite is a mineral of magmatic origin. It crystallizes in the late stages of magma differentiation in large, layered intrusions of mafic and ultramafic rocks. Its formation is closely related to the concentration of copper, nickel, and iron sulfides, in which platinum-group metals are dissolved. ## Mineral Associations This mineral almost always co-occurs with other ore minerals. Its most common associations include base metal sulfides (chalcopyrite, pentlandite, pyrrhotite) and other platinum-group minerals, such as moncheite, merenskyite, sobolevskite, as well as native gold and silver. ## Localities The most important and classic localities for kotulskite are the copper-nickel deposits in the Norilsk region (Talnakh, Oktyabrskoye) in Siberia, Russia. It is also known from the Bushveld Complex in South Africa, the Stillwater Complex in Montana (USA), and the Sudbury region in Canada.

Rarity

Rare

For collectors

## Quality Criteria The quality of kotulskite specimens, which are only available as microscopic preparations, is assessed based on different criteria than for cabinet minerals. The most important factors are the size and "purity" (absence of cracks and impurities) of the analyzed grain, the richness of the paragenesis (presence of other rare minerals in the immediate vicinity), and precise documentation of the locality. The value is purely scientific and collectible in a narrow sense of the word. ## Popular Localities The most prized by specialized scientific collections are specimens (polished sections) from classic localities, especially from the Norilsk region in Russia, where this mineral was first described.

Care and storage

## Cleaning Kotulskite specimens are typically microscopic inclusions in other minerals, often in the form of polished sections or microscopic preparations. Cleaning in the traditional sense is neither necessary nor possible. Polished sections can be very gently wiped with a soft, lint-free cloth to remove dust. ## What to Avoid Avoid any contact with abrasive materials that can scratch the soft surface of the mineral and its surrounding matrix. Also, avoid contact with acids and other aggressive chemicals. ## Storage Microscopic preparations and polished sections containing kotulskite are best stored in special specimen boxes (so-called micro-mount boxes) to protect them from dust and mechanical damage.

Sources

IMA Mineral List (CNMNC)