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.
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.
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
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