Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-26T05:46:45.769Z Has data issue: false hasContentIssue false
  • English
  • Français

Nucleation and growth of iron oxides in olivines, (Mg,Fe)2SiO4

Published online by Cambridge University Press:  05 July 2018

P. E. Champness
P. E. Champness*
Affiliation:
Department of Geology, University of Manchester
Get access Rights & Permissions [Opens in a new window]

Summary

Iron-rich olivines have been oxidized in air in the laboratory and the mechanism of their breakdown has been elucidated using X-ray diffraction and electron microscopy. Low-temperature oxidation (500–800 °C) produces well-oriented hematite- and magnetite-like precipitates together with amorphous silica. The reaction is a cellular one in which thin needles of oxide about 50–100 Å apart grow into the matrix separated by regions of amorphous silica. Nucleation of spherical colonies of the iron oxide and silica occurs on dislocations.

Although the hematite or magnetite always shows the same topotactic relationship with the matrix, the direction in which the needle-like precipitates grow is determined by the orientation of the nucleating dislocation. The small size and highly distorted nature of these precipitates accounts for the diffuseness of their X-ray reflections.

Oxidation at 1000 °C produces undistorted equiaxed grains of the oxides about 0·2 μm in size. They are surrounded by silica, which produces a disordered electron diffraction pattern. As the temperature is raised, the silica achieves more structural order and the oxide grains increase in size.

Type
Research Article
Information
Mineralogical Magazine , Volume 37 , Issue 291 , September 1970 , pp. 790 - 800
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1970

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Barber, (D. J.), 1970. Journ. Materials Sci. 5, 1.CrossRefGoogle Scholar
Bowen, (N. L.), Schairer, (J. F.), and Posnjak, (E.), 1933. Amer. Journ. Sci. 225, 273.CrossRefGoogle Scholar
Brown, (W. L.) and Smith, (J. V.), 1963. Zeitg. Krist. 118, 186.CrossRefGoogle Scholar
Champness, (P. E.), 1968. Ph.D. Thesis, Cambridge University.Google Scholar
Champness, (P. E.) and Gay, (P.), 1968. Nature, 218, 157.CrossRefGoogle Scholar
Christian, (J. W.), 1965. Theory of Transformations in Metals and Alloys, p. 331. Pergamon Press (London).Google Scholar
Deer, (W. A.), Howie, (R. A.), and Zussman, (J.), 1962. Rock-Forming Minerals, 5. Longmans (London).Google Scholar
Gorgeu, (A.), 1885. Compt. Rend. Acad. Sci. Paris, 98, 1281.Google Scholar
Haggerty, (S. E.) and Baker, (L.), 1967. Contr. Min. Petr. 16, 233.CrossRefGoogle Scholar
Holgersson, (S.), 1927. Lunds Univ. Årsskrift, 23, No. 9.Google Scholar
Hugill, (W.) and Green, (A. T.), 1938. Trans. Brit. Ceram. Soc. 37, 279.Google Scholar
Jay, (A. H.), 1944. Min. Mag. 27, 54.Google Scholar
Koltermann, (M.), 1962. Neues Jahrb. Min. Monatsh. 181.Google Scholar
Koltermann, (M.)and Mueller, (K. H.), 1963. Ber. deutsch, keram. Ges. 40, 20.Google Scholar
Posnjak, (E.), 1930. Amer. Journ. Sci. ser. 5, 19, 67.CrossRefGoogle Scholar
Tilley, (C. E.), 1952. Ibid. Bowen vol. 529.Google Scholar
Venables, (J. A.), 1962. Phil. Mag. 7, 35.CrossRefGoogle Scholar
Weatherly, (G. C.) and Nicholson, (R. B.), 1968. Ibid. 17, 801.CrossRefGoogle Scholar
Weiskirchner, (W.), 1958. Rend. Soc. Min. Ital. 14, 355.Google Scholar
Yoder, (H. S.) and Sahama, (Th. G.), 1957. Amer. Min. 42, 475.Google Scholar