Jump to ContentJump to Main Navigation
Show Summary Details
More options …

American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian

IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

See all formats and pricing
More options …
Volume 104, Issue 9


Edscottite, Fe5C2, a new iron carbide mineral from the Ni-rich Wedderburn IAB iron meteorite

Chi Ma
  • Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A
  • Email
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
/ Alan E. Rubin
  • Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California 90095-1567, U.S.A
  • Maine Mineral & Gem Museum, 99 Main Street, P.O. Box 500, Bethel, Maine 04217, U.S.A
  • Other articles by this author:
  • De Gruyter OnlineGoogle Scholar
Published Online: 2019-08-28 | DOI: https://doi.org/10.2138/am-2019-7102


Edscottite (IMA 2018-086a), Fe5C2, is a new iron carbide mineral that occurs with low-Ni iron (kamacite), taenite, nickelphosphide (Ni-dominant schreibersite), and minor cohenite in the Wedderburn 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 (Fe4.73Ni0.23Co0.04)C2.00. The end-member formula is Fe5C2. Electron backscatter diffraction shows that edscottite has the C2/c Pd5B2-type structure of the synthetic phase called Hägg-carbide, c-Fe5C2, which has a = 11.57 Å, b = 4.57 Å, c = 5.06 Å, b = 97.7 °, V = 265.1 Å3, and Z = 4. The calculated density using the measured composition is 7.62 g/cm3. Like the other two carbides found in iron meteorites, cohenite (Fe3C) and haxonite (Fe23C6), 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.

Keywords: Edscottite; Fe5C2; new mineral; iron carbide; Wedderburn iron meteorite

References cited

  • Armstrong, J.T. (1995) CITZAF: A package of correction programs for the quantitative electron beam X-ray analysis of thick polished materials, thin films, and particles. Microbeam Analysis, 4, 177–200.Google Scholar

  • Breen, J.P., Rubin, A.E., and Wasson, J.T. (2016) Variations in impact effects among IIIE iron meteorites. Meteoritics & Planetary Science, 51, 1611–1631.Google Scholar

  • Buchwald, V.F. (1975) Handbook of Iron Meteorites. University of California Press, Berkeley. http://evols.library.manoa.hawaii.edu/handle/10524/33750

  • Fang, C.M., Sluiter, M.H.F., van Huis, M.A., Ande, C.K., and Zandbergen, H.W. (2010) Origin of predominance of cementite among iron carbides in steel at elevated temperature. Physical Review Letters, 105, 055503.Google Scholar

  • Goldstein, J.I., Huss, G.R., and Scott, E.R.D. (2017) Ion microprobe analyses of carbon in Fe-Ni metal in iron meteorites and mesosiderites. Geochimica et Cosmochimica Acta, 200, 367–407.Google Scholar

  • Goodrich, C.A., and Bird, J.M. (1985) Formation of iron-carbon alloys in basaltic magma at Iivfaq, Disko Island: The role of carbon in mafic magmas. Journal of Geology, 93, 475–492.Google Scholar

  • Goodrich, C.A., Ash, R.D., Van Orman, J.A., Domanik, K., and McDonough, W.F. (2013) Metallic phases and siderophile elements in main group ureilites: Implications for ureilite petrogenesis. Geochimica et Cosmochimica Acta, 112, 340–373.Google Scholar

  • Goodrich, C.A., Harlow, G.E., Van Orman, J.A., Sutton, S.R., Jercinovic, M.J., and Mikouchi, T. (2014) Petrology of chromite in ureilites: Deconvolution of primary oxidation states and secondary reduction processes. Geochimica et Cosmochimica Acta, 135, 126–169.Google Scholar

  • Hägg, G. (1934) Pulverphotogramme eines neuen Eisencarbides. Zeitschrift für Kristallographie—Crystalline Materials, 89, 92–94.Google Scholar

  • Jack, K.H., and Wild, S. (1966) Nature of c-carbide and its possible occurrence in steels. Nature, 212, 248–250.Google Scholar

  • Kaminsky, F.V., and Wirth, R. (2011) Iron carbide inclusions in lower-mantle diamond from Juina, Brazil. Canadian Mineralogist, 49, 555–572.Google Scholar

  • Keller, L.P. (1998) A transmission electron microscope study of iron-nickel carbides in the matrix of the Semarkona unequilibrated ordinary chondrite. Meteoritics & Planetary Science, 33, 913–919.Google Scholar

  • Krot, A.N., Zolensky, M.E., Wasson, J.T., Scott, E.R.D., Keil, K., and Ohsumi, K. (1997) Carbide-magnetite assemblages in type-3 ordinary chondrites. Geochimica et Cosmochimica Acta, 61, 219–237.Google Scholar

  • Leineweber, A., Shang, S., Liu, Z., Widenmeyer, M., and Niewa, R. (2012) Crystal structure determination of Hägg carbide, c-Fe5C2 by first-principles calculations and Rietveld refinement. Zeitschrift für Kristallographie—Crystalline Materials, 227, 207–220.Google Scholar

  • Ma, C., and Rubin, A. (2019) Edscottite, IMA 2018-086a. CNMNC Newsletter No. 47, February 2019: 204. European Journal of Mineralogy, 31, 199–204.Google Scholar

  • Retief, J.J. (1999) Powder diffraction data and Rietveld refinement of Hägg-carbide, c-(Fe5C2 Powder Diffraction, 14, 130–132.Google Scholar

  • Reuter, K.B., Williams, D.B., and Goldstein, J.I. (1989) Determination of the Fe-Ni phase diagram below 400°C. Metallurgical Transactions A, 20, 719–725.Google Scholar

  • Scott, E.R.D. (1971) New carbide, (Fe,Ni)23C6 found in iron meteorites. Nature, 229, 61–62.Google Scholar

  • Scott, E.R.D. (1972) Geochemistry, mineralogy and petrology of iron meteorites. Ph.D. thesis, University of Cambridge, U.K.Google Scholar

  • Scott, E.R.D., and Agrell, S.O. (1971) The occurrence of carbides in iron meteorites (abstract). Meteoritics, 6, 312–313.Google Scholar

  • Scott, E.R.D., and Jones, R.H. (1990) Disentangling nebular and asteroidal features of CO3 carbonaceous chondrite meteorites. Geochimica et Cosmochimica Acta, 54, 2485–2502.Google Scholar

  • Simon, S.B., Sutton, S.R., Brearley, A.J., Krot, A.N., and Nagashima, K. (2019) The effects of thermal metamorphism as recorded in CO3.0 through CO3.2 chondrites. Lunar and Planetary Science, 50, abstract 1444.Google Scholar

  • Taylor, G.J., Okada, A., Scott, E.R.D., Rubin, A.E., Huss, G.R., and Keil, K. (1981) The occurrence and implications of carbide-magnetite assemblages in unequilibrated ordinary chondrites (abstract). Lunar and Planetary Science, 12, 1076–1078.Google Scholar

  • Wasson, J.T., and Kallemeyn, G.W. (2002) The IAB iron-meteorite complex: A group, five subgroups, numerous grouplets, closely related, mainly formed by crystal segregation in rapidly cooling melts. Geochimica et Cosmochimica Acta, 66, 2445–2473.Google Scholar

  • Weerasinghe, G.L., Needs, R.J., and Pickard, C.J. (2011) Computational searches for iron carbide in the Earth’s inner core. Physical Review B, 84, 174110.Google Scholar

About the article

Received: 2019-05-06

Accepted: 2019-06-04

Published Online: 2019-08-28

Published in Print: 2019-09-25

FundingOptical microscopy was done at UCLA and Caltech. SEM, EBSD, and EPMA were carried out at the Geological and Planetary Science Division Analytical Facility, Caltech, which is supported in part by NSF grants EAR-0318518 and DMR-0080065. This work was also supported by NASA grants NNX15AH38G and NNG06GF95G.

Citation Information: American Mineralogist, Volume 104, Issue 9, Pages 1351–1355, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2019-7102.

Export Citation

© 2019 Walter de Gruyter GmbH, Berlin/Boston.

Comments (0)

Please log in or register to comment.
Log in