Nickelphosphide

Chemical formula: Ni₃P

Nickelphosphide is a very rare nickel phosphide, occurring as fine, metallic inclusions in iron meteorites.

Nickelphosphide is a mineral from the phosphide group, approved by the IMA in 2000. It occurs as very fine, rounded or irregular grains, usually not exceeding several tens of micrometers in size. It is opaque and has a metallic appearance. ## Characteristics Typical nickelphosphide specimens are microscopic inclusions within other minerals, mainly in iron meteorites. Due to the extremely small size of the crystals, its macroscopic features are not observed. Identification requires advanced analytical techniques, such as electron microscopy and X-ray microanalysis. ## Physical Properties The mineral is characterized by a metallic luster and high density, estimated at 7.37 g/cm³. Hardness has not been measured due to the small grain size, but is estimated based on analogy with its synthetic counterpart to be approximately 6-7 on the Mohs scale. It is opaque, and its streak is grayish-black. ## Colors and Varieties Nickelphosphide is gray to yellowish in color. No varieties of this mineral are distinguished. ## History and Name The name "nickelphosphide" directly refers to its chemical composition – the dominance of nickel and phosphorus. The mineral was first identified in the El Sampal iron meteorite, found in Chubut Province, Argentina. It was described by M.I. Petyaev and collaborators, and subsequently approved by the International Mineralogical Association (IMA) in 2000 under number IMA2000-008. Its synthetic counterpart, Ni₃P, was known in metallurgy long before the discovery of the natural mineral. ## Uses Nickelphosphide has no practical or commercial applications. Its significance is purely scientific, particularly in the fields of meteoritics and planetology, as it provides information about geochemical processes occurring in the parent bodies of asteroids.

Properties

Mohs hardness
6.5-7
Luster
Metallic
Streak
Grayish-black
Density
0
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Identification of nickelphosphide is impossible without specialized equipment. It requires observation on polished sections under a scanning electron microscope (SEM) and confirmation of chemical composition using X-ray microanalysis (EDS/WDS). In reflected light, it has a yellowish tint. ## Distinguishing from Similar Minerals Nickelphosphide can be confused with other phosphides found in meteorites, such as schreibersite ((Fe,Ni)₃P) or nickel-schreibersite ((Ni,Fe)₃P). Differentiation is based solely on precise analysis of the nickel to iron ratio. Nickelphosphide is an end-member of the isomorphic series with schreibersite, in which nickel dominates over iron. ## Crystal Forms The mineral forms very small, rounded or irregular grains, typically ranging from 5 to 50 micrometers in size. It occurs as inclusions within or adjacent to kamacite.

Geological environment

## Genesis Nickelphosphide is a primary mineral that crystallized directly from a metallic melt within the parent bodies of asteroids. Its formation is associated with the slow cooling of planetesimal cores under conditions of very low oxygen fugacity. It is a typical component of iron meteorites. ## Mineral Associations This mineral most commonly occurs in association with kamacite (a variety of nickel-iron), taenite (another variety of nickel-iron), schreibersite, troilite, and graphite. ## Localities Nickelphosphide has been identified in several iron meteorites. The type locality is the El Sampal meteorite (IAB-MG group) found in Argentina. Other confirmed occurrences include the Morasko meteorite (Poland), the Sikhote-Alin meteorite (Russia), and the Uwet meteorite (Nigeria).

Rarity

Extremely rare

For collectors

## Quality Criteria Nickelphosphide is not a collectible mineral in the visual sense. Its value is purely scientific and related to the meteorite in which it occurs. For meteorite collectors, the presence of rare minerals, such as nickelphosphide, can increase the value and attractiveness of a specimen, but only if confirmed by scientific analyses. The mineral itself is invisible to the naked eye. ## Market Prices There is no market for nickelphosphide as a separate mineral. Its value is an integral part of the price of the meteorite in which it is found. This price depends on the type of meteorite, its size, history, and provenance, rather than on the presence of microscopic inclusions of a specific mineral. ## Popular Localities From a scientific and collecting perspective (in the context of meteorites), the most well-known localities are the find sites of meteorites in which it has been identified, such as El Sampal (Argentina), Morasko (Poland), and Sikhote-Alin (Russia).

Care and storage

## Cleaning Due to their microscopic size and occurrence as inclusions, nickelphosphide specimens are not cleaned in the traditional sense. All procedures are carried out under laboratory conditions on polished metallographic sections. ## What to Avoid Contact with strong acids, which can react with the mineral and its surrounding matrix, should be avoided. As a component of iron meteorites, specimens containing nickelphosphide should be protected from moisture to prevent rusting (oxidation) of the surrounding iron. ## Storage Storing meteorite specimens containing nickelphosphide requires controlled conditions. They should ideally be kept in a dry environment, for example, in containers with a desiccant (silica gel), to minimize the risk of corrosion.

External references

Sources

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