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Edscottite, Fe_5C_2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite

Ma, Chi and Rubin, Alan E. (2019) Edscottite, Fe_5C_2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite. American Mineralogist, 104 (9). pp. 1351-1355. ISSN 0003-004X. https://resolver.caltech.edu/CaltechAUTHORS:20190904-090734912

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Abstract

Edscottite (IMA 2018-086a), Fe_5C_2, is a new iron carbide mineral that occurs with low-Ni iron (kamacite), taenite, nickelphosphide (Ni-dominant schreibersite), and minor cohenite in the Wedder-burn iron meteorite, a Ni-rich member of the group IAB complex. 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 (Fe_(4.73)Ni_(0.23)Co_(0.04))C_(2.00). The end-member formula is Fe_5C_2. Electron backscatter diffraction shows that edscottite has the C2/c Pd_5B_2-type structure of the synthetic phase called Hägg-carbide, χ-Fe_5C_2, which has a = 11.57 Å, b= 4.57 Å, c = 5.06 Å, β = 97.7 °, V = 265.1 Å^3, and Z = 4. The calculated density using the measured composition is 7.62 g/cm^3. Like the other two carbides found in iron meteorites, cohenite (Fe_3C) and haxonite (Fe_(23)C_6), edscottite forms in kamacite, but unlike these two carbides, it forms laths, possibly due to very rapid growth after supersaturation of carbon. Haxonite (which typically forms in carbide-bearing, Ni-rich members of the IAB complex) has not been observed in Wedderburn. Formation of edscottite rather than haxonite may have resulted from a lower C concentration in Wedderburn and hence a lower growth temperature. The new mineral is named in honor of Edward (Ed) R.D. Scott, a pioneering cosmochemist at the University of Hawai‘i at Manoa, for his seminal contributions to research on meteorites.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.2138/am-2019-7102DOIArticle
http://www.minsocam.org/MSA/AmMin/TOC/2019/Sep2019_data/AM-19-97102.zipPublisherSupporting Information
ORCID:
AuthorORCID
Ma, Chi0000-0002-1828-7033
Alternate Title:Edscottite, Fe5C2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite
Additional Information:© 2019 Mineralogical Society of America. Manuscript received May 6, 2019; Manuscript accepted June 4, 2019; Manuscript handled by Ian Swainson. We thank Ed Scott for discussions and insightful comments. We thank Alex Ruzicka, Cyrena Goodrich and Tim McCoy for their constructive reviews. Deposit item AM-19-97102, Supplemental Material. Deposit items are free to all readers and found on the MSA website, via the specific issue’s Table of Contents (go to http://www.minsocam.org/MSA/AmMin/TOC/2019/Sep2019_data/Sep2019_data.html).
Subject Keywords:Edscottite, Fe5C2, new mineral, iron carbide, Wedderburn iron meteorite
Issue or Number:9
Record Number:CaltechAUTHORS:20190904-090734912
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190904-090734912
Official Citation:Chi Ma, Alan E. Rubin; Edscottite, Fe5C2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite. American Mineralogist ; 104 (9): 1351–1355. doi: https://doi.org/10.2138/am-2019-7102
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98406
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:04 Sep 2019 17:00
Last Modified:09 Mar 2020 13:19

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