Crystallographic Changes Accompanying the Verwey Transition in a Magnetite from Steatite

The crystallographic structural analysis of the magnetite of a steatite rock at 298 K, (saturation magnetization, σ = 95.0 J T-1 kg-1) showed two cubic networks and, below Verwey temperature (TV ca.120 K) a monoclinic structure, basing on their cell dimensions and different transitional behaviors when reducing the temperature. A monoclinic structure was identified from their cell dimensions and different transition behaviors when reducing the temperature. The average chemical formula of this almost stoichiometric magnetite was deduced from the chemical analysis, 298 K-Mössbauer and the structural refinement. The Rietveld fitting of the 298 K X-ray pattern is Fe 3 + Fe 0 . 95 3 + Fe 0 . 88 2 + Cr 0 . 04 3 + Al 0 . 04 3 + Mg 0 . 05 2 + Ni 0 . 02 2 + ⊗ 0 . 02 O 4, where [ ] and { } stand for cations in tetrahedral and octahedral coordination symmetries, respectively. The crystallographic structure below TV in this magnetite was observed from synchrotron X-ray diffraction data (XRD), collected at 15 K. It was identified three structures: two cubic (space group, Fd3m), with significantly different lattice parameters, and one monoclinic (P2/c).