Chemists and mineralogists often have to elucidate the crystal structure of new materials even when conventional X-ray methods are not applicable. If, for example, long-range order is not extensive or the amount of material available for examination is minute (<10-7 g) the classical techniques of X-ray or neutron diffraction cannot be used. In such circumstances, direct structural determination using high resolution electron microscopy is, in principle, possible. To achieve worthwhile information, however, a point-to-point resolution of 2.8 Å or better is desirable, if the structural details of most oxides, halides, chalcogenides and various oxysalts of metallic and semi-metallic elements are to be established. We demonstrate here how high voltage, high resolution electron microscopy confirms the struc ture of a representative silicate mineral, showing the potential of the technique for the elucidation of locally abnormal (at the subunit cell level) structures.
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