Four new structure refinements of olivine

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Abstract
Mg/Fe order in olivine has been suggested from x-ray data (Finger, 1969/70) and proven with Mössbauer spectra (Bush et al., 1970). New structure refinements on four magnesium-rich olivines give two to ten times improved values for extinction coefficients, atomic positions, anisotropic temperature factors, site occupancies, and formal charges. The parameters have been refined from x-ray data by least-squares methods imposing proper constraints of chemical composition and electrostatic neutrality on derivatives. R factors range between 2 and 3%. Lunar samples show significant (twenty standard deviations) order of Fe on the smaller M(1) site [52% Fe on M(1), 48% Fe on M(2)], metamorphic forsterites are essentially disordered. Formal charges have been determined: Fe,Mg = +0.3, Si = +0.2, O = −0.2. The extinction coefficient, a sensitive measure for structural defects, is much lower for specimens from lunar dust, which show radiation damage and possible effects of shock deformation. Mean M(1)–O and M(2)–O distances increase linearly with Fe/(Fe + Mg).