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Magnetite exsolution in almandine garnet

Published online by Cambridge University Press:  05 July 2018

A. J. Brearley  and
P. E. Champness
A. J. Brearley
Affiliation:
Department of Geology, The University, Manchester, M13 9PL
P. E. Champness
Affiliation:
Department of Geology, The University, Manchester, M13 9PL
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Abstract

Three almandine-rich metamorphic garnets have been studied by analytical electron microscopy and electron microprobe analysis. Electron microprobe analyses with total Fe calculated as Fe2+ show that there are no significant departures from stoichiometry due to the presence of Fe3+ in any of the garnets studied. However, in the transmission electron microscope (TEM) all the garnets were found to contain myriad spherical, iron-rich particles up to 400 Å in diameter. Microdiffraction techniques have revealed that the particles are a cubic spinel phase, consistent with magnetite. There is no crystallographic relationship between the host garnet and the particles, a rare situation for exsolution processes. The presence of such particles is interpreted in terms of the exsolution of magnetite from almandine garnet during cooling. This can apparently occur at temperatures below 55°C. The size of the particles is a qualitative indicator of the cooling rate of the rock, but is also dependent on the original Fe3+ content of the host garnet.

Keywords

magnetitealmandinegarnetexsolutiontransmission electron microscopy
Type
Silicate mineralogy
Information
Mineralogical Magazine , Volume 50 , Issue 358 , December 1986 , pp. 621 - 633
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1986

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References

Aines, R.D., and Rossman, G.R. (1984) Am. Mineral, 69, 1116-26.Google Scholar
Ashworth, J.R. (1979) Mineral. Mag, 43, 535-8.CrossRefGoogle Scholar
Atherton, M.P. (1977) Scott. J. Geol, 13, 331-70.CrossRefGoogle Scholar
Barber, D.J. (1970) J. Mater. Sci, 5, 1-8.CrossRefGoogle Scholar
Bosworth, T.O. (1910) Q. J. Geol. Soc, 66, 376.CrossRefGoogle Scholar
Brearley, A.J. (1984) Petrological and electron optical studies of metamorphic reactions.Ph.D. thesis. Univ. of Manchester.Google Scholar
Chadwick, G.A. (1972) Metallography of phase transformations. Butterworths.Google Scholar
Champness, P.E., and Lorimer, G.W. (1971) Contrib. Mineral. Petrol, 33, 171-83.CrossRefGoogle Scholar
Cliff, G., and Lorimer, G.W. (1975) J. Microsc, 103, 203-7.CrossRefGoogle Scholar
Powell, D.J., Pilkington, R., Champness, P.E., and Lorimer, G.W. (1983) Inst. Phys. Conf. Ser.No. 68. 63-6.Google Scholar
Cressey, G. (1978) Nature, 271, 533-4.CrossRefGoogle Scholar
Greenwood, H.J. (1975) Am. J. Sci, 275, 573-93.CrossRefGoogle Scholar
Grimes, N.W., Thompson, P., and Kay, H.F. (1983) Proc. R. Soc. Land, A386, 333-45.Google Scholar
Hollister, L.S. (1969) Geol. Soc. Am. Bull, 80, 2465-94.CrossRefGoogle Scholar
Joesten, R. (1983) Am. J. Sci, 283A, 233-54.Google Scholar
Lorimer, G.W. (1983) X-ray microanalysis.In Quantitative Electron Microscopy.Proc. of Institute of Physics— NATO 25th Scottish Universities Summer School in Physics.Google Scholar
MacKenzie, W.S., and Guilford, C. (1981) Atlas of rock-forming minerals. Longmans, London.Google Scholar
Michael, J.R., Cliff, G., and Williams, D.B. (1984) Scanning Electron Microscopy, 4, 1697-705.Google Scholar
Mongkoltip, P., and Ashworth, J.R. (1983) Am. Mineral, 68, 143-55.Google Scholar
Moseley, D. (1981) . Ibid. 66, 976-9.Google Scholar
Moseley, D. (1984. Ibid. 69, 139-53.CrossRefGoogle Scholar
Shannon, R.D., and Prewitt, C.T. (1969). Acta Crystallogr, 25, 925-46.CrossRefGoogle Scholar
Smith, P.P.K. (1978) Phil. Mag, 38, 99-102.CrossRefGoogle Scholar
Steeds, J.W., and Evans, N.S. (1980) Proc. 38th EMSA Meeting, 188-91.Google Scholar