Nipalarsite

Chemical formula: Ni₈Pd₃As₄

An extremely rare nickel palladium arsenide with a metallic luster, found as microscopic grains in copper-nickel sulfide deposits.

## Characteristics Nipalarsite is a very rare arsenide mineral, chemically classified as a nickel palladium arsenide. It occurs almost exclusively as microscopic, anhedral grains or inclusions within other ore minerals, mainly sulfides. It typically does not form crystals visible to the naked eye. Its appearance is typical of ore minerals – it has a metallic luster and a steel-gray or tin-white color, sometimes with a yellowish tint. ## Physical Properties This mineral is opaque and characterized by a strong, metallic luster. Its Mohs hardness is approximately 5, placing it in the same category as apatite. It is a very dense mineral, with a density calculated from its chemical composition and crystal structure of 9.97 g/cm³, which is a result of the high content of heavy metals – palladium and nickel. ## Colors and Varieties Nipalarsite has a uniform, metallic color, described as tin-white or steel-gray. No color varieties or commercial varieties are known. ## History and Name The mineral was first described in 1993 by E.M. Spiridonov, T.L. Evstigneeva, and V.V. Konyushok. Its name is derived from its chemical composition and is an acronym of the elements it contains: **NI**ckel, **PAL**ladium, and **ARS**enic. ## Applications Nipalarsite has no industrial applications. Its significance is purely scientific and collectible, as a rare component of mineral parageneses in platinum-group element (PGE) deposits.

Properties

Mohs hardness: 5
Luster: Metallic
Streak: Black
Density: 9.97
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Identification of nipalarsite is impossible without advanced analytical techniques. In practice, recognition involves chemical analysis in a micro-area (e.g., using an electron microprobe – EDS/WDS) of a polished rock section. Auxiliary features for targeting samples for analysis include: metallic luster, high density, occurrence within Cu-Ni ores rich in platinum-group elements, and paragenesis with other palladium and platinum minerals. ## Distinguishing from Similar Minerals Nipalarsite is visually indistinguishable from many other rare platinum-group minerals (PGM) with a metallic, silvery luster, such as sobolevskite, kotulskite, sperrylite, or atokite. It can also be confused with more common sulfides, like pentlandite. Definitive differentiation is only possible based on chemical composition. ## Crystal Forms This mineral forms exclusively anhedral (irregular) grains ranging in size from fractions of a micrometer to about 0.2 mm. It occurs as isolated inclusions or forms complex aggregates with other PGE minerals, often as rims around chalcopyrite or pentlandite grains.

Geological environment

## Genesis Nipalarsite is a magmatic mineral, crystallizing at high temperatures. It forms during sulfide segregation processes within large intrusions of mafic and ultramafic rocks (e.g., gabbro, norite, peridotite), which are sources of copper, nickel, and platinum-group element (PGE) deposits. ## Mineral Associations This mineral occurs in close association with other ore minerals. It most commonly co-occurs with chalcopyrite, pentlandite, and pyrrhotite. It is also accompanied by other rare PGE minerals, such as kotulskite, sobolevskite, sperrylite, atokite, rustenburgite, as well as native metals (gold, silver). ## Localities As an extremely rare mineral, nipalarsite has been identified in only a few locations worldwide, which are also major mining areas for Cu-Ni-PGE ores. The type locality is the Oktyabrskoye deposit in the Noril'sk region (Siberia, Russia). It has also been found in the Bushveld Complex in South Africa and in some deposits in China.

Rarity

Extremely rare

For collectors

## Quality Criteria Nipalarsite is a mineral of interest exclusively to specialized collectors of rare species (so-called "species collectors") and scientific institutions. Specimens typically consist of polished sections or rock fragments with microscopic inclusions. The value of a specimen is determined not by aesthetics, but by the analytically confirmed presence of the mineral, its abundance in the sample, and the association with other rare PGE minerals. ## Popular Localities The most known and classic specimens, serving as reference material, come from the discovery locality – the Noril'sk-Talnakh region in Russia. Material from this area is highly valued by collectors specializing in this group of minerals.

Care and storage

## Cleaning Nipalarsite specimens, typically microscopic inclusions in the host rock, generally do not require cleaning. If dust removal is necessary, a soft brush or compressed air can be used. For heavier soiling, careful wiping with a damp cloth and distilled water is permissible. ## What to Avoid Avoid contact of the mineral with strong acids and other aggressive chemicals, which can react with arsenides and sulfides. Do not use ultrasonic cleaners or steam cleaning. Despite a hardness of 5, avoid cleaning with abrasive materials. ## Storage Nipalarsite is a stable mineral. Store it in dry conditions, in sealed containers or display cases, to protect it from dust and mechanical damage. It is not sensitive to light.

Sources

IMA Mineral List (CNMNC)