The iron-oxide system can be used as a marker of oxidized and reduced conditions in closed systems. However, natural rocks with iron oxide minerals also exhibit such reactions, although the natural system is typically open. To understand the behaviour of this natural system, some similarities were investigated, in terms of crystallographic textures, between the microstructures of two systems: natural open system and synthetic closed system of iron oxide phase transformation. Particular cases of phase transformation in iron oxide minerals, described as natural reactions of magnetite to hematite and synthetic reactions of hematite to magnetite, were chosen. It is observed, in both scenarios, that the transformation obeys the topotaxial and epitaxial relationship, which are well described for the iron oxide system. However, in natural open systems, the precipitation of a new phase during the in situ transformation modifies the microstructures and must be taken into account as an important factor to describe them.
Magnetite Iron Oxide Hematite Wustite Crystallographic Plane
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The authors would like to acknowledge the Center of Microscopy at the Universidade Federal de Minas Gerais (http://www.microscopia.ufmg.br) and MICROLAB at the Universidade Federal de Ouro Preto for providing the equipment and technical support for experiments involving electron microscopy. We are grateful to Jamie Beaulieu by the technical support in the Rock Mechanics Laboratory at Brown University and Breno Barbosa for his technical assistance in Center of Microscopy.
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