Abstract
Single crystals of a rock magnetite were separated from steatite cobbles collected in a geological site near the city of Serro (18° 36′ 47′′ S 43° 22′ 46′′ W), Minas Gerais, Brazil. A typically well-shaped magnetite single crystal was characterized by chemical analysis, 57Fe Mössbauer spectrometry at 300, 77 and 4 K and under an applied magnetic field of 6 T at 10 K, magnetization measurements and electronic microprobe. From Mössbauer data, the sample is stoichiometric with a tetrahedral and octahedral site occupancy ratio of 1:2. Elemental chemical analysis and point-to-point electron microscope probing show some inclusions of lamellar ilmenite (≤ 1 mass%) randomly distributed throughout the magnetite matrix, and also that the magnetite matrix is constituted only by Fe2+ and Fe3+, with no isomorphic substitution. Results are discussed on the basis of the magnetization curve and of the temperature dependence of the AC magnetic susceptibility. The Verwey transition occurs in the temperature range of 100–115 K, observed by a sudden change in the temperature dependence of the magnetization.
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Received: 27 August 2001 / Accepted: 30 January 2003
Acknowledgements This work was supported by Brazilian agencies FAPEMIG (grant CEX 1123/90) and CAPES. ACD is grateful to FAPEMIG and CAPES for providing a doctoral fellowship. We also thank Dr. L. G. Knauer (IGC-UFMG) for his help in the sample acquisition and Dr. G. P. Santana (DQ-FUA) for his contribution in the Mössbauer discussion and his constant encouragement.
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Doriguetto, A., Fernandes, N., Persiano, A. et al. Characterization of a natural magnetite. Phys Chem Minerals 30, 249–255 (2003). https://doi.org/10.1007/s00269-003-0310-x
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DOI: https://doi.org/10.1007/s00269-003-0310-x