High-resolution transmission-electron-microscopy observation of the ultra-fine structure of natural magnetite

Abstract

The microstructure of natural magnetite found in the Panzhihua mountain in China was studied by means of high-resolution transmission electron microscopy (HRTEM). Electron diffraction patterns show lattice modulations along the [110] direction of wiistite co-existing with magnetite. Such a one-dimensional superstructure, with a lattice parameter of 2.6ao, is the characteristic feature of an incommensurate structure. It is related to the nonstoichiometric phase P' of Feo.92oO that results from a deficiency of Fe atoms in the wfistite. The structural images exhibit the intergrowth of the magnetite matrix and the wiistite. The wavelike ultra-fine structure in wiJstite suggests that the superstructure is possibly coincident with the displacive lattice modulation. Basal and nonbasal domains, which result from the random distribution of Fe atoms during the initial stage of nucleation of magnetite during the geological aging of wfistite, are also revealed in the structural images and are discussed on the basis of the structure of magnetite.

Structural and morphological anomalies in magnetosomes: possible biogenic origin for magnetite in ALH84001

“…Type 1 pseudo‐hexagonal prismatic magnetosomes were rarely twinned (< 1%) (data not reported). The relative structural and compositional purity of the pseudo‐hexagonal prismatic magnetosomes analysed here possibly reflects the advanced α‐Proteobacterial lineage of the bacteria that produce them (Spring et al ., 1992; Spring et al ., 1994; Spring & Schleifer, 1995; Spring et al ., 1998). Small lobous outgrowths twinned in the {1 1 1} lattice plane were common in mature D‐shaped magnetosomes.…”

“…Magnetotactic bacteria have been detected in marine, brackish and freshwater sediments (Blakemore, 1982;Mann et al ., 1990), the water column of a stratified lake (Bazylinski et al ., 1995) and soil (Fassbinder et al ., 1990). Magnetofossils have compositional and structural homogeneity, being predominantly in the SD‐ and SP‐size ranges (Petersen et al ., 1986 and Butler & Banerjee, 1975), whereas petrogenic magnetites are compositionally and structurally impure with greatly varying sizes (Wang et al ., 1994).…”

Ordering of Octahedral Vacancies in Transition Aluminas

“…Such an assignment of image dots modulates the original crystal, and the periodicities of modulation are determined in the micrograph to be 1.59 and 1.18 nm, along the [010] and [001] directions, respectively. In the 〈100〉 projected spinel structure, channels surrounded by cations and anions are 0.28 nm apart in the 〈011〉 directions, 6 so that the image dots in Fig. 3 may correspond to these channel positions.…”

Discovery of the recoverable high-pressure iron oxide Fe4O5

“…Coexisting wüstite and magnetite exhibit extensive degrees of nonstoichiometry and complex defect structures, depending on the synthesis temperature and cooling path. The two cubic phases share the same oxygen array and can grow coherently (8,20,21), providing a nearly continuous range of structures with random defect distributions, clustered defects, and coherently grown distinct phases. The high-pressure behavior of the binary phase diagram is relatively unexplored.…”