A meteorite found in Australia — called the Wedderburn iron meteorite because of where it was found — contains edscottite, an iron-carbide mineral never seen in nature before.
Scanning electron microscopy image (colorized) showing edscottite in the polished Wedderburn section from the UCLA Meteorite Collection. Image credit: Ma Rubin, doi: 10.2138/am-2019-7102.
The Wedderburn iron meteorite was found as a single mass on a road just outside Wedderburn in Victoria, Australia, in 1951.
The space rock was a well rounded monolith with the overall dimensions of 5 x 3.6 x 2.6 cm and weighed 210 g.
Recently, researchers from Caltech, the University of California, Los Angeles (UCLA) and Maine Mineral Gem Museum teamed up to perform mineralogical investigation of Wedderburn.
During an analysis of a polished thick section of the meteorite from the UCLA Meteorite Collection, they identified a new iron-carbide mineral, Fe5C2, which they named edscottite.
“Edscottite is a new iron-carbide, Fe5C2, joining the other two carbides found in iron meteorites, cohenite and haxonite, as a naturally occurring, approved mineral,” they said.
“The mineral name is in honor of Edward R.D. Scott, a pioneering cosmochemist at the University of Hawai’i at Manoa, for his multifaceted contributions to research on meteorites.”
To characterize its chemical composition, structure, and associated phases, the authors used high-resolution scanning electron microscopy, electron backscatter diffraction, and electron probe microanalysis.
“Edscottite occurs as subhedral, lath-shaped or platy single crystals, 0.8 x 15 mm to 1.2 x 40 mm and 4 x 18 mm in size,” they said.
“The mean chemical composition of edscottite determined by electron probe microanalysis is (wt%) Fe 87.01, Ni 4.37, Co 0.82, C 7.90, total 100.10, yielding an empirical formula of (Fe4.73Ni0.23Co0.04)C2.00. The end-member formula is Fe5C2.”
“The mineral appears white microscopically in reflected light. The calculated density using the measured composition is 7.62 g/cm3.”
“Edscottite precipitates in steels, where it is called Hägg-carbide,” they noted.
The scientists believe the mineral was created in the core of another planet.
“Like cohenite and haxonite, edscottite forms in low-Ni iron (known as kamacite in the meteorite literature), but unlike these two carbides, it forms laths, possibly due to very rapid growth after supersaturation of carbon,” they said.
A paper on the discovery was published in the journal American Mineralogist.
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Chi Ma Alan E. Rubin. 2019. Edscottite, Fe5C2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite. American Mineralogist 104 (9): 1351-1355; doi: 10.2138/am-2019-7102
