Isomertieite

Chemical formula: Pd<sub>11</sub>Sb<sub>2</sub>As<sub>2</sub>

Isomertieite is a rare palladium arsenide and antimonide, occurring as fine, metallic grains in ultramafic rocks.

## Characteristics Isomertieite is a very rare mineral from the arsenide and antimonide group. It forms extremely small, most often anhedral (irregular) grains, rarely exceeding 0.1 mm in size. It is usually observed as inclusions within other minerals, mainly chromite. It is opaque, with a metallic luster and a creamy-white color with a pinkish hue. ## Physical Properties Due to the extremely small size of the grains, most physical properties, such as hardness, density, cleavage, or fracture, have not been precisely determined. The luster is distinctly metallic, and the mineral is completely opaque. ## Colors and Varieties This mineral is homogeneous in composition and does not form color varieties. Its color in reflected light is characteristic – creamy-white with a pinkish or pinkish-brown hue. ## History and Name The name "isomertieite" refers to its relationship with the mineral mertieite-I (Pd₈(Sb,As)₃). It is a polymorph of mertieite-I, meaning it has the same chemical composition but crystallizes in a different crystallographic system (isometric, whereas mertieite-I is hexagonal). It was first described in 1974 by L.J. Cabri and J.H.G. Laflamme based on material from Itabira, Brazil. ## Applications Isomertieite has no industrial applications. Its significance is purely scientific and collectible, as a very rare mineral from the platinum-group elements.

Properties

Mohs hardness
5.5
Luster
Metallic
Streak
Black
Density
11.23
Cleavage
None
Transparency
Opaque
Crystal system
Cubic

Diagnostic features

## Identification Identification of isomertieite is possible only with advanced laboratory techniques, such as reflected light ore microscopy and chemical analysis using an electron microprobe (EDS/WDS). Its characteristic feature is a creamy-white color with a pinkish hue. It is isotropic. ## Distinguishing from Similar Minerals It can be confused with other platinum-group minerals, such as mertieite-I, mertieite-II, stibiopalladinite, or genkinite. Differentiation requires analysis of chemical composition and optical properties in reflected light. Isomertieite is distinguished by its isometric crystallographic system and specific composition (Pd₁₁Sb₂As₂). ## Crystal Forms It usually occurs as very small, irregular grains. Poorly formed, cubic or octahedral crystals, not exceeding several tens of micrometers, are rarely observed.

Geological environment

## Genesis Isomertieite forms in magmatic deposits, in ultramafic rocks such as dunites and pyroxenites, often serpentinized. It is a hydrothermal or late-magmatic phase mineral, crystallizing at relatively low temperatures. ## Mineral Associations It most often co-occurs with chromite, in which it forms inclusions. It is also accompanied by other platinum-group minerals, such as mertieite-I, mertieite-II, atokite, rustenburgite, palladoarsenide, stibiopalladinite, as well as pentlandite, chalcopyrite, and magnetite. ## Localities The most important occurrences of this mineral include the Bushveld Complex in South Africa (Maandagshoek farm), deposits in Itabira (Minas Gerais, Brazil), the Stillwater Complex in Montana (USA), and nickel and copper deposits near Norilsk and on the Kola Peninsula in Russia.

Rarity

Very rare

For collectors

## Quality Criteria Due to their microscopic nature, isomertieite specimens are not evaluated for aesthetics. The highest value is placed on samples where the presence of the mineral has been confirmed by chemical analysis. The attractiveness of a specimen is enhanced by a rich association with other rare platinum-group minerals and a well-documented, classic locality. ## Popular Localities The most prized by specialized collectors are specimens from type localities, such as Itabira in Brazil and the Bushveld Complex in South Africa, from which the best-studied samples originate.

Care and storage

## Cleaning Isomertieite specimens, due to the microscopic size of the grains, practically do not require cleaning. If they are on a larger rock matrix, it can be gently cleaned with compressed air or a soft-bristled brush. Avoid contact with water and chemical agents. ## What to Avoid Avoid all chemicals, acids, and ultrasonics, which could damage both the microscopic isomertieite grains and the surrounding minerals. Do not heat the specimen or expose it to rapid temperature changes. ## Storage Isomertieite specimens are best stored in specialized "micromount" boxes, which protect them from dust, moisture, and mechanical damage. Due to its rarity, each specimen should be properly labeled with its locality.

Sources

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