Yixunite

Chemical formula: Pt<sub>₃</sub>In

Yixunite is a rare, naturally occurring platinum-indium alloy, found as small, metallic grains in ultramafic rocks.

## Characteristics Yixunite is an extremely rare mineral from the native elements group, being a natural alloy (intermetallic compound) of platinum and indium. It occurs as very small, rounded or irregular grains, usually not exceeding 0.2 mm in size. Due to its composition, it has a metallic appearance and a steel-gray color with a yellowish tint. ## Physical Properties As a metallic mineral, Yixunite is opaque and possesses a strong, metallic luster. It is characterized by a very high density, approximately 17.68 g/cm³, which is typical for platinum group minerals. Its Mohs hardness is estimated at 5. ## History and Name The mineral was discovered and described in 1995 by Yu Zuxiang. Its name comes from the discovery locality in Yixian County (also known as Yi County or Yixun) in Hebei Province, China. It was approved by the International Mineralogical Association (IMA) in 1994 (IMA number 1994-012). ## Applications Yixunite has no industrial application due to its extreme rarity and microscopic size. Its significance is purely scientific and as a collector's item, as a unique natural compound of platinum and indium.

Properties

Mohs hardness: 5
Luster: Metallic
Streak: Black
Density: 17.68
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of yixunite is impossible without advanced laboratory techniques. It requires analysis by electron microprobe (EDS/WDS) to confirm its chemical composition (platinum and indium). Visually, in polished sections, its steel-gray color with a yellowish tint and strong metallic luster can be observed under a reflected light microscope. ## Distinguishing from similar minerals It can be confused with other platinum group minerals (PGM), such as native platinum, isoferroplatinum, or other intermetallic compounds. Differentiation relies solely on precise chemical composition analysis. ## Crystal forms Yixunite crystallizes in the isometric system, forming an AuCu₃-type structure. It occurs exclusively as anhedral (irregular), rounded grains intergrown with other minerals.

Geological environment

## Genesis Yixunite forms in ultramafic rocks, particularly in chromitites associated with ophiolite complexes. Its presence is a result of magmatic processes during which platinum group elements become concentrated. ## Mineral associations It coexists with other platinum group minerals and sulfides. It is most commonly associated with chromite, native platinum, iridium, osmium, rutile, as well as minerals such as laurite, irarsite, erlichmanite, and cuproiridsite. ## Localities The type and only confirmed locality for yixunite is the chromitite deposits in the ophiolite complex in Yixian County, Hebei Province, northern China.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of a yixunite specimen is determined solely by its scientific and documentary value. Since the mineral is microscopic, specimens have no aesthetic appeal. The most valuable samples are those where the presence of yixunite has been analytically confirmed, originating from the type locality. The richness of associations with other rare platinum group minerals enhances its value. ## Popular localities The only source of specimens is the type locality in China. The mineral is not available on the commercial collector's market and is mainly found in the collections of scientific institutions and museums.

Care and storage

## Cleaning Specimens containing microscopic yixunite grains can only be cleaned mechanically, using a soft brush or paintbrush to remove dust. The use of water or any chemical agents is not recommended to avoid damaging the host rock. ## What to avoid Avoid contact with chemicals, acids, and cleaning agents. The rock containing yixunite should be protected from moisture and extreme temperatures. ## Storage Specimens should be stored under stable conditions, preferably in a closed, dry container or display cabinet, away from direct sunlight and dust. Due to the microscopic nature of the mineral, it is recommended to include a label with the precise location of the grains on the specimen.

Sources

IMA Mineral List (CNMNC)