Palladothallite

Chemical formula: Pd₃Tl

Palladothallite is a very rare palladium-thallium alloy, occurring as microscopic, metallic grains.

## Characteristics Palladothallite is a very rare mineral from the metal alloy group. It forms extremely small, rounded or irregular grains, usually not exceeding 0.1 mm in size. Due to its size, its visual features are difficult to observe without the use of specialized equipment, such as an electron microscope. In reflected light, it presents a creamy white color with a pinkish hue. ## Physical Properties As a metallic mineral, palladothallite is characterized by a strong, metallic luster. It is opaque. Its hardness and density have not been precisely measured due to the small size of the grains, but the density calculated based on the chemical formula and unit cell parameters is 13.05 g/cm³. ## History and Name The mineral was first described in 1982 by T. L. Evstigneeva, A. D. Genkin, V. A. Kovalenker, N. V. Trubkin, T. V. Burova, and I. P. Laputina. Its name directly refers to its chemical composition – the presence of palladium (pallado-) and thallium (-thallite). It was approved by the International Mineralogical Association (IMA) in the same year. The type locality (locus typicus) is the Oktyabrskoye copper-nickel deposit in the Norilsk region of Siberia, Russia.

Properties

Luster
Metallic
Density
13.04
Cleavage
None
Transparency
Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Identification of palladothallite is only possible using advanced laboratory techniques, such as ore microscopy in reflected light and chemical analysis using an electron microprobe (EDS/WDS). Its characteristic feature is a creamy white color with a pinkish hue in reflected light. ## Distinguishing from Similar Minerals It can be confused with other microscopic metal minerals from the platinum-group elements (PGE) or metal alloys that often co-occur with it, such as atokite, rustenburgite, or palladoarsenide. Definitive differentiation requires chemical composition analysis, which will show the dominance of palladium and thallium. ## Crystal Forms Palladothallite occurs as anhedral (lacking crystal faces), rounded or irregular grains and inclusions in other minerals, mainly in chalcopyrite and other sulfides.

Geological environment

## Genesis Palladothallite forms as a result of hydrothermal processes within copper-nickel sulfide deposits associated with mafic and ultramafic intrusions. It crystallizes in the late stages of mineralization, forming inclusions in sulfides. ## Mineral Associations This mineral co-occurs with chalcopyrite, talnakhite, cubanite, magnetite, atokite, rustenburgite, palladoarsenide (Pd₂As), polarite, majakite, and other platinum-group minerals. ## Locations The only confirmed occurrence of palladothallite in the world is its type locality – the Oktyabrskoye copper-nickel deposit, in the Talnakh area, near Norilsk on the Putorana Plateau, Siberia, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria Palladothallite is not a mineral collected in the traditional sense. Its value is purely scientific. Specimens consist of rock fragments (most often sulfides) containing microscopic, identified grains of palladothallite. The most valuable samples are those from the type locality, with the largest number of confirmed grains, documented by analyses.

Care and storage

## Cleaning Due to their microscopic size and extreme rarity, palladothallite specimens are not subjected to standard cleaning. They are typically preserved as polished sections for microscopic examination or left in their original rock matrix. ## What to Avoid Any chemicals, ultrasonics, and mechanical cleaning should be avoided, as they could irreversibly destroy or remove the microscopic mineral grains from the substrate. ## Storage Specimens should be stored under stable conditions, in specialized boxes protecting them from dust, moisture, and mechanical damage. It is best to keep them in their original rock matrix.

External references

Sources

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