Gaotaiite

Chemical formula: Ir<sub>₃</sub>Te<sub>₈</sub>

Gaotaiite is an extremely rare iridium telluride, forming microscopic, metallic inclusions in platinum-group minerals.

## Characteristics Gaotaiite is an iridium telluride, belonging to the group of extremely rare minerals. It occurs as very fine, anhedral (irregular) grains, usually not exceeding 0.1 mm in size. It is observed as inclusions in other minerals, mainly bornite. Due to its microscopic size, visual characteristics are difficult to determine without specialized equipment. In reflected light under a polarizing microscope, it has a creamy-yellow color and exhibits weak pleochroism. ## Physical Properties As an opaque mineral, it is characterized by a strong, metallic luster. Its hardness and density have not been precisely measured due to the small size of the grains; however, its Vickers hardness (VHN) is 101 kg/mm², which suggests a Mohs hardness in the range of 2.5-3. The density calculated based on the chemical formula and unit cell parameters is 9.55 g/cm³. ## History and Name The mineral was discovered in the Gaotai nickel-copper deposit in China and described in 1995 by Chinese mineralogists Yu Zuxiang, Zhou Kefa, and Lin Shizhen. Its name comes directly from its type locality (place of discovery). It was approved by the International Mineralogical Association (IMA) in the same year (IMA1995-015).

Properties

Mohs hardness: 2.5-3
Luster: Metallic
Density: 9.55
Cleavage: None
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of gaotaiite is possible only through advanced laboratory techniques. Preliminary identification under a ore microscope is based on its creamy-yellow color in reflected light, high reflectivity, and anisotropy. Final confirmation requires chemical analysis by electron microprobe (EDS/WDS) to determine the presence of iridium and tellurium in appropriate proportions. ## Distinguishing from similar minerals It can be confused with other microscopic tellurides or precious metal sulfides, such as moncheite (PtTe₂), maslovite (PtBiTe), or kotulskite (PdTe). Differentiation is possible only based on precise chemical composition analysis. ## Crystal forms Gaotaiite forms exclusively anhedral, irregular grains and aggregates, often with rounded or oval shapes. It has not been observed in the form of well-developed crystals.

Geological environment

## Genesis Gaotaiite is a hydrothermal mineral associated with copper, nickel, and platinum-group element (PGE) ore deposits. It forms in the late stages of crystallization, at relatively low temperatures, in a tellurium-rich environment. In its type locality, it occurs in bornite-chalcopyrite veins cutting gabbroic rocks. ## Mineral associations This mineral coexists with bornite (in which it forms inclusions), chalcopyrite, moncheite, kotulskite, hessite, sobolevskite, sperrylite, cherepanovite, irarsite, native iridium, and gold-silver alloys. ## Localities The only confirmed and described occurrence of gaotaiite in the world is its type locality - the Gaotai Cu-Ni deposit, in Hannan District, Sichuan Province, China.

Rarity

Extremely rare

For collectors

## Quality criteria Gaotaiite does not occur in macroscopic specimens, so its collector value is purely scientific and systematic. Highly prized are rock fragments (polished thin sections) with thoroughly studied and documented presence of this mineral, preferably in association with other rare tellurides. The value of a specimen is directly proportional to the quality of the analysis confirming its identity.

Care and storage

## Cleaning Due to its microscopic size and occurrence as inclusions within the host rock, individual gaotaiite grains are not subject to cleaning. The host rock specimen can be mechanically cleaned using a soft brush and distilled water, taking care not to damage the surface. ## What to avoid Contact with strong acids and chemicals that could react with tellurides or surrounding minerals should be avoided. There is no detailed information on sensitivity to light or temperature, but standard caution is recommended as with other rare minerals. ## Storage Specimens containing gaotaiite should be stored under stable conditions, in sealed containers or display cases, to protect them from dust and mechanical damage. Accurate labeling indicating the presence of this rare mineral is important.

Sources

IMA Mineral List (CNMNC)