Pseudomertieite

Chemical formula: Pd<sub>5+x</sub>(Sb,As)<sub>2-x</sub> (x = 0.1-0.2)

Pseudomertieite is an extremely rare palladium arsenide and antimonide, occurring as microscopic, metallic grains.

## Characteristics Pseudomertieite is a platinum-group mineral (PGM), occurring as small, irregular (anhedral) grains, usually not exceeding 200 micrometers in size. It is opaque, with a creamy-white or tin-white color and a strong metallic luster. It is usually strongly intergrown with other palladium and platinum minerals, forming complex aggregates. ## Physical Properties The hardness of the mineral is estimated at approximately 5-5.5 on the Mohs scale. It has a high density of 10.97 g/cm³, which is typical for minerals with a high palladium content. It is brittle and does not exhibit cleavage. In reflected light under a polarizing microscope, its color is creamy-white. ## Colors and Varieties The mineral is uniform in color, adopting a creamy-white to tin-white hue. No color varieties or commercial varieties are distinguished. ## History and Name It was described in 1975 by Louis J. Cabri, J. H. Gilles Laflamme, and J. M. Stewart. Its name refers to its chemical similarity to mertieite-II, with which it was initially confused. The prefix "pseudo-" refers to its different, orthorhombic crystallographic symmetry, in contrast to the hexagonal symmetry of mertieite-II. ## Applications Due to its extreme rarity and microscopic size, pseudomertieite has no industrial applications. It is solely an object of scientific research and is valued by specialized collectors of rare minerals (so-called microminerals).

Properties

Mohs hardness
5-5.5
Luster
Metallic
Density
10.97
Cleavage
None
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Certain identification of pseudomertieite is impossible without advanced analytical techniques. This requires chemical composition analysis using an electron microprobe (EDS/WDS) and confirmation of the crystal structure by X-ray diffraction (XRD). Visually, as a metallic, creamy-white grain, it is indistinguishable from many other platinum-group minerals. ## Distinguishing from Similar Minerals It can be confused with other palladium arsenides and antimonides, such as mertieite-II, isomertieite, as well as palladoarsenide, palladobismutharsenide, or native platinum-group metals. Differentiation is based solely on laboratory data regarding composition and crystal symmetry. ## Crystal Forms Pseudomertieite occurs exclusively in the form of anhedral (irregular, lacking crystal faces) grains, usually with rounded outlines. No well-formed crystals have been observed.

Geological environment

## Genesis Pseudomertieite forms under magmatic conditions, in ultramafic rocks, especially within layered mafic and ultramafic intrusions. It is found in chromitite deposits. It can also occur in placer deposits as a secondary mineral, released by the weathering of host rocks. ## Mineral Associations It co-occurs with other platinum-group minerals, such as atheneite, isomertieite, palladoarsenide, palladobismutharsenide, as well as chromite, magnetite, and various silicates. ## Localities The type locality is the Cauê iron mine in Itabira (Minas Gerais, Brazil). Its presence has also been confirmed in placer deposits of the Tulameen River (British Columbia, Canada), in the Bushveld Complex (South Africa), and within the Great Dyke (Zimbabwe).

Rarity

Extremely rare

For collectors

## Quality Criteria For such a rare micromineral, the main criterion of value is the certainty of identification confirmed by analysis and the richness of the paragenesis, i.e., the presence of other rare PGM minerals on the same specimen. The size of the pseudomertieite grain is also important – the larger it is, the more valuable the specimen is for research and systematic collections. ## Popular Localities The most classic and frequently cited specimens in the literature come from the type locality in Itabira, Brazil. Research material has also been obtained from the Bushveld Complex in South Africa.

Care and storage

## Cleaning Pseudomertieite specimens are typically microscopic grains embedded in the host rock, which do not require cleaning. If necessary, dust can be removed with a gentle stream of compressed air. Contact with water and any chemical agents should be avoided. ## What to Avoid The mineral is stable, but ultrasonic cleaners, chemicals, acids, and sudden temperature changes should be avoided. The main threat is physical damage to the delicate host specimen. ## Storage Specimens should be stored in stable conditions, away from dust and moisture. The best solution is a dedicated micromount box, which protects against mechanical damage and contamination.

Sources

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