Abstract
Jacobsite from Weabonga, N.S.W., of composition Mn0.980Mg0.006Fe2.009O4.000 corresponds closely to the ideal composition. A precise determination of the cubic cell-edge by extrapolation gave 8.5050 ± 0.0005 A. The great variation among cell-edge determinations of artificial preparations is discussed. It may arise from oxygen present in excess of stoichiometric formula requirements, shown to be absent from the mineral studied, or from variations in the distribution of the cations in the spinel structure of jacobsite. The smaller cell edge relative to normal type spinel structures does not necessarily indicate for jacobsite the presence of the inverse type structure.
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