HIGH-RESOLUTION TRANSMISSION-ELECTRON-MICROSCOPY OBSERVATION OF THE ULTRA-FINE STRUCTURE OF NATURAL MAGNETITE

The microstructure of natural magnetite found in the Panzhihua mountai n in China was studied by means of high-resolution transmission electr on microscopy (HRTEM). Electron diffraction patterns show lattice modu lations along the [110] direction of wustite co-existing with magnetit e. Such a one-dimensional superstructure, with a lattice parameter of 2.6a0, is the characteristic feature of an incommensurate structure. I t is related to the nonstoichiometric phase P' of Fe0.920O that result s from a deficiency of Fe atoms in the wustite. The structural images exhibit the intergrowth of the magnetite matrix and the wustite. The w avelike ultra-fine structure in wustite suggests that the superstructu re is possibly coincident with the displacive lattice modulation. Basa l and nonbasal domains, which result from the random distribution of F e atoms during the initial stage of nucleation of magnetite during the geological aging of wustite, are also revealed in the structural imag es and are discussed on the basis of the structure of magnetite.