Magnetic properties of other mineral systems

  • W. O’Reilly


Haematite is a much studied and little understood material, and to extract what might be considered the intrinsic magnetic properties, relevant to its role as a remanence carrier, from the body of available data is problematical. It seems that microstructure and extrinsic influences affect more than just the magnetization process parameters in the case of haematite. One problem is that ideal haematite has only a weak magnetization, about 0.5 percent of that of magnetite, and the measured properties of haematite samples are correspondingly susceptible to (say) the distorting effect of undetectable quantities of magnetic contaminants. Studies on highly specified crystals have tended to concentrate on the antiferromagnetic properties, and such experiments are largely irrelevant to the fine-grain remanence-carrying haematite of rock samples. Studies of fine particle samples, prepared by crushing larger crystals, by oxidizing magnetite or by the decomposition or dehydration of a suitable iron-bearing compound, produce a range of values of saturation magnetization (after high field susceptibility has been allowed for). The magnetization also is found to fall after high temperature treatment, in air, of some of the studied material. An absolute prerequisite for an interpretable study of the intrinsic properties or magnetization process in haematite is an exhaustive characterization of the sample material. However, it may be that magnetic properties are more sensitive to (say) the presence of small quantities of maghemite than are other analytical techniques, and only indirect assessment of the material may be possible.


Basal Plane Coercive Force Spin Structure Mineral Magnetism Spontaneous Magnetization 
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© Blackie & Son Ltd 1984

Authors and Affiliations

  • W. O’Reilly
    • 1
  1. 1.University of Newcastle upon TyneUK

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