Murchisite

Chemical formula: Cr<sub>5</sub>S<sub>6</sub>

Murchisite is an extremely rare chromium sulfide, discovered as microscopic grains in the famous Murchison meteorite.

## Characteristics Murchisite is a chromium sulfide with a metallic luster. It occurs exclusively as extremely small, submicron or micron-sized grains that do not form crystals visible to the naked eye. Its observation is only possible using advanced microscopic techniques, such as scanning electron microscopy. ## Physical Properties Due to the microscopic size of the grains, most physical properties have not been experimentally determined. The mineral is opaque and has a metallic luster. The density calculated based on its chemical composition and crystal structure is approximately 4.13 g/cm³. Hardness, cleavage, and fracture are unknown. ## Colors and Varieties No color varieties or commercial forms have been described. Microscopic observations indicate a metallic appearance typical of sulfides. ## History and Name The mineral's name comes from the Murchison meteorite, in which it was first identified. This meteorite, a carbonaceous chondrite, fell in 1969 near the town of Murchison in Victoria, Australia. Murchisite was officially approved as a new mineral by the International Mineralogical Association (IMA) in 2017. ## Applications Murchisite has no commercial or industrial applications. Its significance is purely scientific, providing information about the processes of mineral formation in the primordial solar nebula.

Properties

Luster
Metallic
Density
4.13
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Identification of murchisite is only possible using advanced analytical methods, such as electron microprobe (EDS/WDS) to determine chemical composition, and electron or X-ray diffraction for crystal structure analysis. ## Distinguishing from Similar Minerals On a microscopic scale, it can be confused with other chromium or iron sulfides. Definitive distinction requires precise analysis of the chemical composition (chromium to sulfur ratio). ## Crystal Forms It is observed as anhedral (irregularly shaped) grains ranging in size from submicron to several micrometers.

Geological environment

## Genesis Murchisite is a mineral of extraterrestrial origin. It formed under conditions prevalent in the early Solar System, before the formation of planets. It crystallized in calcium-aluminum-rich inclusions (CAIs) within a CM2-type carbonaceous chondrite. ## Mineral Associations In the Murchison meteorite, it co-occurs with hibonite, spinel, perovskite, and iron-chromium sulfides. ## Localities The only confirmed locality of murchisite in the world is the Murchison meteorite, which fell in Australia.

Rarity

Extremely rare

For collectors

## Quality Criteria Not applicable. Murchisite does not form collectible specimens. Its value is purely scientific. ## Market Prices Not applicable. The mineral is not traded on the collector's market. ## Popular Localities The only locality is the Murchison meteorite. Fragments of this meteorite are highly valued by collectors, but this value stems from its origin and scientific significance, not from the presence of macroscopic specimens of specific minerals.

Care and storage

## Cleaning Not applicable. The mineral occurs as microscopic inclusions within the meteorite rock and is not isolated as separate specimens. ## What to Avoid Not applicable. ## Storage Fragments of the Murchison meteorite containing murchisite are stored in scientific and museum collections under stable, controlled conditions, protecting them from contamination and degradation.

Sources

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