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 field gradient (EFG) tensors for Fe²⁺ at the M1 sites, Fe²⁺ at the M2 sites, and Fe³⁺ at the M1 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 Fe²⁺ at the M1 sites in Wo₅₀ 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 Fe²⁺ at the M1 sites of Wo₄₀ Ca–rich pyroxene was different from the Wo₅₀. Whereas principal axes of EFG tensors for Fe²⁺ at the M1 sites of Wo₅₀ pyroxenes had the same direction, principal axes of V_XX and V_YY of EFG of Wo₄₀ had different directions from that from Wo₅₀. The difference of intensity and EFG tensors between Wo₅₀ and Wo₄₀ suggests that the intensity and EFG tensors for Fe²⁺ at M1 sites are dependent on the Ca contents and are independent of Fe contents. Some intensity and EFG tensors for Fe²⁺ at the M2 sites and Fe³⁺ at the M1 sites in Ca–rich pyroxene were also obtained. However, the compositional dependence of the intensity and EFG tensors has yet to be clarified, because the number of examples is insufficient.