If magnetite and hematite transform into each other they keep the close-packed O framework and obviously use partial dislocation movement to change between hexagonal and cubic stacking sequence. Rearrangement and diffusion of Fe ions cause a transformation from cubic to trigonal symmetry. The virtual dominance of the close-packed {111} and {0001} planes are usually the major argument of the transformation mechanism and result in the common conclusion that the often observed foliation during transformation displays {111} planes of magnetite. Unfortunately, trace analysis of the hematite foliation in magnetite grains with a diameter of approximately 1-2mm (rock sample containg some minor minerals like quartz, fluorite, apatite) reflects that practically all macroscopically discovered traces fit to {110} planes of magnetite, and only a very small amount of short traces (around 5%) match the predicted {111}. EDS element distribution maps show traces of Si and Ca parallel to {110} so that they could be used as argument for the observed foliation. However, are these traces the result of the magnetite growth (zoning), or more an argumentation for a diffusion into magnetite? Both could perhaps cause lattice distortions which could simplify the diffusitivity of Fe along these planes. Is there anybody who observed similar effects, or has any idea how to explain the discrepancy between the microscopic transformation and the macroscopically visible transformation progress?
Hi Gert, with such set of data it is hard to answer, but it may be easy to solve by diffussion and growths experiment. Sure that you can give relative large pieces of both minerals with right planes (may be polished) to Institute of Experimental Mineralogy http://www.iem.ac.ru/general.html , or in Germany
This is lamer opinion but better than nothing )
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