Anduoite

Chemical formula: RuAs<sub>₂</sub>

Anduoite is a very rare ruthenium arsenide with a metallic luster, found in ultramafic chromite rocks.

## Characteristics Anduoite is an extremely rare mineral from the arsenide group. It occurs as very small, irregular grains, usually less than 0.2 mm in size, disseminated in chromitite. Its grains are too small for crystalline forms to be observed with the naked eye. It has a steel-gray to lead-gray color and is opaque. ## Physical Properties This mineral is characterized by a strong, metallic luster. Its hardness on the Mohs scale is estimated at 6.5 to 7, making it a relatively hard mineral. It is a brittle mineral. ## History and Name Anduoite was discovered in 1974 in a chromite deposit in Amdo (Anduo) County, Tibet (China), from which its name is derived. It was described by Chinese mineralogists Yu Zuxiang and Zhou Xuexin and approved by the International Mineralogical Association (IMA) in 1979. ## Uses Due to its extreme rarity and microscopic size, anduoite has no industrial applications. It is solely an object of scientific and collecting interest for specialized institutions and micromineral collectors.

Properties

Mohs hardness: 6.5-7
Luster: Metallic
Streak: Black
Density: 11.03
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of anduoite is impossible without advanced laboratory techniques. In polished sections under a reflected light microscope, it can be recognized by its high reflectivity, color, and hardness. Final confirmation requires chemical analysis (e.g., using an electron microprobe) to confirm the presence of ruthenium and arsenic. ## Differentiation from Similar Minerals It can be confused with other platinum-group minerals and arsenides of similar appearance, such as sperrylite (PtAs₂) or other minerals from the löllingite group. Differentiation relies solely on chemical composition analysis. ## Crystal Forms Anduoite forms exclusively anhedral (irregular), rounded grains. Well-formed crystals have not been observed.

Geological environment

## Genesis Anduoite forms under specific conditions within ultramafic igneous intrusions, in chromite-rich rocks (chromitites). Its presence is associated with magmatic processes and subsequent hydrothermal alterations in an environment rich in arsenic and platinum-group metals. ## Mineral Associations This mineral occurs in association with chromite (as the host rock), as well as other platinum-group minerals such as irarsite, osarsite, rutenarsenite, laurite, iridarsenite, and also with native osmium, iridium, platinum, and pentlandite and other sulfides. ## Localities In addition to the type locality in Amdo, Tibet (China), anduoite has been identified in chromite deposits in the Bushveld Complex in South Africa, in the ultramafic massif in the Polar Urals in Russia, as well as in Albania and Myanmar. All these occurrences are extremely rare and are of scientific interest only.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an anduoite specimen is determined almost exclusively by its confirmed authenticity through analysis. Since it occurs as microscopic grains, collector specimens are usually fragments of the host rock (chromitite) with identified and labeled anduoite grains, often in the form of polished sections. The size and abundance of these grains on a given fragment increase its value for specialized collectors. ## Popular Localities The most "classic" specimens, though extremely rare, come from the discovery site in Tibet. Specimens from other confirmed localities, such as Bushveld or the Urals, are equally valuable from a scientific perspective.

Care and storage

## Cleaning Specimens containing anduoite, typically in the form of polished sections or small fragments of host rock, should only be cleaned with compressed air to remove dust. All contact with water and chemicals should be avoided. ## What to Avoid As an arsenide, this mineral may be sensitive to moisture and oxidation. Contact with acids and other chemical agents should be avoided. It should not be heated or subjected to ultrasound. ## Storage It is recommended to store specimens in a dry environment, preferably in sealed plastic containers (so-called micromount boxes) or in capsules with a desiccant, to prevent chemical degradation.

Sources

IMA Mineral List (CNMNC)