Chenmingite

Chemical formula: Fe₂+Cr₃+₂O₄

Chenmingite is an extremely rare iron and chromium oxide, a natural analogue of ferrous chromite, discovered in the Suizhou meteorite.

## Characteristics Chenmingite is a mineral from the spinel group, representing a natural, ferrous iron (Fe²⁺)-rich analogue of chromite. It was identified as microscopic, subhedral grains ranging from 15 to 30 micrometers in size. It occurs as inclusions in other minerals, mainly in chromite. Due to its size, its visual characteristics cannot be assessed with the naked eye. ## Physical Properties Due to the microscopic size of the grains, most physical properties, such as hardness, density, luster, or transparency, have not been experimentally determined. Based on crystallographic data, its density was calculated to be 5.16 g/cm³. It is an opaque mineral with a metallic luster and a black color and streak. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2017 (IMA 2017-036). The name honors Chen Ming (born 1963), a researcher from the Institute of Geochemistry in Guangzhou (Chinese Academy of Sciences), for his contributions to the study of extraterrestrial minerals, including the discovery of several new minerals in meteorites. ## Applications Chenmingite has no industrial or commercial applications. Its significance is purely scientific, as an indicator of the conditions prevailing during the formation of meteorite parent bodies.

Properties

Luster: Metallic
Streak: Black
Density: 5.16
Cleavage: None
Transparency: Opaque
Crystal system: Isometric

Diagnostic features

## Identification Identification of chenmingite is possible only through advanced laboratory techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron microprobe analysis (EMPA). In backscattered electron (BSE) images, it differs from the surrounding chromite by a slightly brighter shade, which results from a higher average atomic number (greater iron content). ## Distinguishing from similar minerals Chenmingite is a member of the spinel group and represents the end-member of an isomorphic series with chromite (FeCr₂O₄) and hercynite (FeAl₂O₄). Distinguishing it from chromite requires precise chemical analysis showing the dominance of Fe²⁺ ions over Mg²⁺ in the A position of the spinel structure. It is a natural analogue of synthetic ferrous chromite. ## Crystal forms It has only been observed as very small, irregular or partially formed (subhedral) grains.

Geological environment

## Genesis Chenmingite forms under conditions of strong reduction and high temperature. In the Suizhou meteorite, it was identified in shock veins, where it likely crystallized from an impact melt or transformed from primary chromite as a result of shock metamorphism processes that occurred during a cosmic collision. ## Mineral associations This mineral occurs in close association with chromite (as its rim or vein), troilite, kamacite, taenite, graphite, and various silicates, such as olivine and pyroxene. ## Localities The only confirmed occurrence (type locality) of chenmingite in the world is the Suizhou meteorite – an L6 ordinary chondrite that fell in 1986 in Hubei Province, China.

Rarity

Extremely rare

For collectors

## Quality criteria Chenmingite is not available on the collector's market as a separate mineral. Its value is purely scientific. The only way to own it in a collection is to acquire a fragment of the Suizhou meteorite in which it was identified. In such a case, the value of the specimen is determined by the characteristics of the meteorite itself (size, history, preservation of the fusion crust), and not by the presence of microscopic chenmingite grains.

Care and storage

## Cleaning Due to its microscopic nature and occurrence as inclusions within other minerals, individual chenmingite grains are not subject to cleaning. ## What to avoid Meteorite specimens containing chenmingite should be protected from moisture, which can cause corrosion of metallic phases, and from strong chemicals and acids, which could damage the entire sample. ## Storage Specimens of the Suizhou meteorite, in which chenmingite was found, should be stored under stable conditions, preferably in a dry environment (e.g., in a container with a desiccant), to prevent degradation of the entire specimen.

Sources

IMA Mineral List (CNMNC)