Arsenopalladinite

Chemical formula: Pd<sub>8</sub>As<sub>3</sub>

Arsenopalladinite is a rare palladium arsenide, forming small, metallic grains and flakes, found in platinum-group element deposits.

## Characteristics Arsenopalladinite is a very rare mineral from the arsenide group. It occurs as very small, anhedral (not exhibiting its own crystallographic forms) grains or flakes, usually less than 1 mm in size. Its appearance is metallic, with a color ranging from white to steel-gray, often with a creamy tint. It is typically intergrown with other platinum-group minerals or sulfides. ## Physical Properties This mineral is characterized by a strong, metallic luster. It is opaque. Due to the small size of the grains, precise determination of hardness and density is difficult; hardness is estimated at approximately 5 on the Mohs scale. It is a brittle mineral. ## Colors and Varieties Arsenopalladinite has a consistent, characteristic color in shades of creamy white to steel-gray. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1974 by C.E. Feather, directly refers to its chemical composition – arsenic (arseno-) and palladium (-palladinite). It was originally described based on material from a platinum mine in the Potgietersrus region (now Mokopane) in the Bushveld Complex, South Africa. ## Applications Arsenopalladinite has no industrial applications. Its significance is purely scientific and collectible, as a component of rich platinum-group element ores.

Properties

Mohs hardness
5
Luster
Metallic
Streak
Black
Density
10.4
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Triclinic

Diagnostic features

## Identification Identification of arsenopalladinite is possible almost exclusively through advanced laboratory methods, such as micro-area analysis (EDS/WDS) in a scanning electron microscope. Preliminary identification under a reflected light microscope is based on its creamy-white color, strong metallic luster, and co-occurrence with other platinum-group minerals. It exhibits weak anisotropy in polarized light. ## Distinguishing from Similar Minerals It can be confused with other bright platinum-group minerals (PGM), such as sperrylite, native platinum, or other palladium arsenides and antimonides. Definitive differentiation requires chemical composition analysis. ## Crystal Forms Arsenopalladinite crystals are extremely rare and microscopic in nature. It typically forms irregular, anhedral grains, flakes, or veinlets as inclusions in other minerals.

Geological environment

## Genesis Arsenopalladinite is a mineral of magmatic origin. It forms as a result of crystallization from residual, platinum-group element (PGE)-rich sulfide melts within large, layered mafic and ultramafic intrusions. It is one of the late-crystallizing minerals in such systems. ## Mineral Associations It most commonly co-occurs with other platinum-group minerals, such as braggite, sperrylite, native platinum, as well as with base metal sulfides like chalcopyrite, pentlandite, and pyrrhotite. ## Localities The most important and classic localities for this mineral are found in the Bushveld Igneous Complex in the Republic of South Africa, especially in the Merensky Reef area. It is also found in other large layered intrusions, such as the Stillwater Complex in Montana (USA) and in nickel and copper deposits in the Norilsk region and the Kola Peninsula in Russia.

Rarity

Very rare

For collectors

## Quality Criteria The quality of an arsenopalladinite specimen is determined almost exclusively by the richness and size of the grains visible under the microscope within the host rock. Since this mineral does not form aesthetic crystals, its collectible value is primarily scientific. Samples with accurately studied and confirmed presence of the mineral, originating from the type locality (South Africa), are most highly prized. ## Popular Localities Specimens from the Bushveld Complex in South Africa, which is the type locality for this mineral, are by far the most valued by specialized collectors.

Care and storage

## Cleaning Arsenopalladinite specimens are usually not cleaned due to their microscopic nature and embedding in the host rock. Any mechanical or chemical intervention risks destroying the tiny grains. If dust removal is necessary, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with any chemicals, especially acids. Do not subject it to ultrasonic cleaning or washing in water. Protect it from scratching and impacts. ## Storage Arsenopalladinite specimens are best stored in their original, sealed "micromount" box, protecting them from dust, moisture, and mechanical damage. Exposure to light is not harmful.

Sources

Read more