Compositional dependence of intensity and electric field gradient tensors for Fe2+ at the M1 site in Ca–rich pyroxene by single crystal Mössbauer spectroscopy

Abstract

The compositional dependence of the intensity and electric fi eld gradient (EFG) tensors for Fe 2+ at the M 1 sites, Fe 2+ at the M 2 sites, and Fe 3+ at the M 1 sites in Ca – rich pyroxene were obtained from Mössbauer spectra of crystallographically oriented single – crystal thin sections of four Ca – rich natural pyroxenes. Components of the intensity tensor ( I XX , I YY , I XY , and I ZZ ) for Fe 2+ at the M 1 sites in Wo 50 Ca – rich pyroxene were almost the same; the averages of the I XX , I YY , I XY , and I ZZ components were 0.342, 0.477, 0.039, and 0.681, respectively. Intensity tensor for Fe 2+ at the M 1 sites of Wo 40 Ca – rich pyroxene was di ff erent from the Wo 50 . Whereas principal axes of EFG tensors for Fe 2+ at the M 1 sites of Wo 50 pyroxenes had the same direction, principal axes of V XX and V YY of EFG of Wo 40 had di ff erent directions from that from Wo 50 . The di ff erence of intensity and EFG tensors between Wo 50 and Wo 40 suggests that the intensity and EFG tensors for Fe 2+ at M 1 sites are dependent on the Ca contents and are independent of Fe contents. Some intensity and EFG tensors for Fe 2+ at the M 2 sites and Fe 3+ at the M 1 sites in Ca – rich pyroxene were also obtained. However, the compositional dependence of the intensity and EFG tensors has yet to be clari fi ed, because the number of examples is insu ffi