Edscottite, Fe_5C_2, a New Iron Carbide Mineral from the Wedderburn Iron Meteorite

Abstract

The Wedderburn iron meteorite, found as a single 210-g mass in Victoria, Australia in 1951, is a Ni-rich ataxite belonging to subgroup sLH of the IAB complex (Low-Au, High-Ni subgroup). It is one of the most Ni-rich irons known (23.4 wt.% Ni [1]), initially classified as group IIID. During a re-investigation of a polished thick section of Wedderburn, we identified a new iron-carbide mineral, Fe5C2 with the C2/c Pd5B2-type structure, named “edscottite” (Fig. 1). Field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron back-scatter diffraction (EBSD) and electron probe microanalysis (EPMA) were used to characterize edscottite and associated phases. This mineral was first identified in Wedderburn [2,3]; synthetic Fe_5C_2 was previously known (e.g., [4-6]). We report here the first natural occurrence of Fe_5C_2 in an iron meteorite as a new carbide mineral. Edscottite (IMA 2018-086a) was approved by the IMA-CNMNC [7]. The mineral name is in honor of Edward (Ed) R. D. Scott, University of Hawai‘i, USA, for his seminal contributions to meteorite research. He discovered haxonite, (Fe,Ni)_(23)C_6 [8] as well as this new iron carbide [2,3].