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3.3 i Electronic and magnetic properties of P21/c clinopyroxenes in the system MgSiO3-FeSiO3 (C.A. McCammon, in collaboration with S.G. Eeckhout and E. De Grave/Gent)

The wide occurrence of pyroxenes in mineral assemblages has motivated a large number of studies to investigate the relation between composition, crystal structure and physical and chemical properties. Simple systems allow the effects of specific variables to be isolated, which has motivated our choice of the system MgSiO3-FeSiO3. The electronic and magnetic properties of orthopyroxene have been well characterized, but the properties of low clinopyroxene with space group P21/c have not been extensively studied.

Samples of P21/c clinopyroxene with varying composition were synthesised in the system MgSiO3-FeSiO3 using a multianvil press at 10 GPa and 1200°C. Run products were examined by electron microprobe and X-ray diffraction. Mössbauer spectra are being collected at temperatures from 0.3 - 773 K in magnetic fields up to 16 T, and complementary SQUID measurements are being carried out at 2 - 300 K.

We have calculated site-specific Mössbauer Debye temperatures which are crucial to the determination of accurate site distributions, and show that the recoil-free fraction for the M1 site is slightly larger than the value for the M2 site. Crystal field parameters have been calculated using the temperature dependence of the quadrupole splitting, and parameters are consistent with the greater distortion of the M2 site. Magnetic properties are a strong function of composition, and in contrast to orthopyroxene, magnetic ordering is not complete even at 0.3 K. Further work is underway to correlate these results with structural data.

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