Ferric Iron Content of Mineral Inclusions in Diamonds from São Luiz: A View into the Lower Mantle

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Science  17 Oct 1997:
Vol. 278, Issue 5337, pp. 434-436
DOI: 10.1126/science.278.5337.434

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Mössbauer spectroscopy on inclusions in diamonds from São Luiz, Brazil, show that (Mg,Fe)O inclusions contain little Fe3+ (Fe3+/ΣFe ≤ 7%), whereas inclusions with pyroxene composition (believed to have been originally in the perovskite structure) and tetragonal almandine-pyrope phase (TAPP) inclusions contain high relative amounts of Fe3+ (Fe3+/ΣFe = 20 to 75%). These observations are consistent with high-pressure experiments on synthetic samples and support the idea that the inclusions originated in the lower mantle. Fe-Mg partitioning data for co-existing (Mg,Fe,Al)(Si,Al)O3 – (Mg,Fe)O pairs also indicate that the phases were in equilibrium at the time of diamond formation in the lower mantle.

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