Chihmingite

Chemical formula: Ni₂+Al₂O₄

Chihmingite is an extremely rare, green mineral of the spinel group, occurring as microscopic grains in a single locality worldwide.

## Characteristics Chihmingite is a nickel member of the spinel supergroup, chemically being a nickel aluminate. It is an extremely rare mineral, identified so far only as microscopic, anhedral grains not exceeding 20 micrometers in size. It occurs as inclusions within corundum crystals. Due to its size, its visual characteristics are observable only under high magnification. ## Physical Properties The hardness of the mineral has not been measured directly but is calculated to be 7.5-8 on the Mohs scale, which is typical for minerals of the spinel group. Similarly, the density, 4.42 g/cm³, is a theoretical value. Chihmingite is transparent and exhibits a vitreous luster. ## Colors and Varieties The observed chihmingite grains are green. No other color varieties or commercial forms of this mineral are known. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2017. Its name honors Chih-Ming Lee, a Taiwanese mineral collector who discovered the type material. The only known occurrence (type locality) is a chromitite body within the Dongqiao ophiolite in Tibet (China). ## Uses Due to its extreme rarity and microscopic size, chihmingite has no commercial or industrial applications. It serves solely as an object of scientific research.

Properties

Mohs hardness: 7.5-8 (obliczona)
Luster: Vitreous
Streak: Undetermined
Density: 4.42 (obliczona)
Cleavage: Not applicable
Fracture: Not applicable
Transparency: Transparent
Crystal system: Isometric

Diagnostic features

## Identification Identification of chihmingite is impossible without advanced analytical techniques. Due to the microscopic size of the grains, its recognition requires the use of an electron microscope with an EDS or WDS analyzer to precisely determine its chemical composition. This is the only method that allows for certain confirmation of the presence of this mineral. ## Differentiation from Similar Minerals Chihmingite can be confused with other green minerals of the spinel group, such as hercynite or gahnospinel, as well as other nickel-bearing spinels (e.g., trevorite). Visually, it is indistinguishable from other fine, green inclusions. Key to differentiation is demonstrating the dominance of nickel and aluminum in the spinel structure. ## Crystal Forms This mineral has been found exclusively as anhedral (irregular, poorly formed) grains. No euhedral (well-formed) crystals have been observed to date.

Geological environment

## Genesis Chihmingite forms under specific geological conditions. It has been found in a chromitite body that is part of an ophiolite complex. Ophiolites are fragments of oceanic crust and the Earth's upper mantle that have been obducted onto continental crust. The presence of chihmingite in such an environment indicates metamorphic or metasomatic processes occurring at high temperatures and pressures, in an environment rich in chromium, nickel, and aluminum. ## Mineral Associations This mineral occurs as an inclusion in corundum. It coexists directly with chromite, as well as with other nickel minerals such as bunsenite, trevorite, and nickeline. ## Localities The only confirmed locality for chihmingite worldwide is the Dongqiao ophiolite, Amdo, Nagqu in the Tibet Autonomous Region, China.

Rarity

Extremely rare

For collectors

## Quality Criteria Given that chihmingite is a microscopic mineral, traditional collector criteria such as size, color, or crystal clarity do not apply. The value of a specimen is purely scientific and depends on confirming the presence of the mineral through analysis. Such specimens are almost exclusively acquired by research institutions and museums as type material. ## Popular Localities The only known locality is the type locality in Tibet. The mineral is not collected for hobbyist purposes.

Care and storage

## Cleaning Chihmingite specimens exist exclusively as microscopic inclusions within a host mineral (corundum) and do not occur in a form that would allow for independent cleaning. Any cleaning procedures apply to the entire corundum specimen and are performed under laboratory conditions. ## What to Avoid As a member of the spinel group, the mineral is likely sensitive to strong acids. The host specimen should be protected from chemicals, extreme temperatures, and mechanical shocks. ## Storage Specimens containing chihmingite are stored in specialized research collections, often as polished thin sections for microscopic analysis. They require protection from dust and physical damage.

Sources

IMA Mineral List (CNMNC)