A new crystallographic technique has been developed, which has been applied to the problem of locating the cations in a natural olivine crystal with the composition (Mg0.90Fe0.10Ni0.004Mn 0.002)2SiO4. The method uses the variation of characteristic x-ray emission with the direction of an exciting electron beam in an analytical transmission electron microscope. It may be applied to nanometer-sized areas and to concentrations as low as 0.1 atomic percent, is capable of distinguishing neighbors in the periodic table, and does not require external standards. The iron atoms in this crystal are evenly distributed between the two available crystal sites M1 and M2 (49.6 ± 1 percent on M1), whereas the trace elements nickel and manganese occupy the M1 and M2 positions, respectively (97 ± 5 percent nickel on M1 and 1 ± 5 percent manganese on M1).
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