An Intensity Tensor and Electric Field Gradient Tensor for Fe3+ at M1 Sites of Aegirine–Augite Using Single-Crystal Mössbauer Spectroscopy

Abstract

An intensity tensor of quadrupole doublets and an electric field gradient tensor for Fe3+ at M1 sites in aegirine–augite ((Ca0.16Na0.86)∑1.02(Mg0.13Fe2+0.04Fe3+0.72 Al0.07)∑0.96Si2.01O6) are determined using single-crystal Mössbauer spectroscopy. The components of the intensity tensor are IXX = 0.670 (19), IYY = 0.353 (14), IXY = −0.113 (37) and IZZ = 0.477 (33). The components of the electric field gradient tensor (VXX, VYY and VZZ) for Fe3+ at M1 sites in aegirine–augite are −5.96 × 109, −4.65 × 1010 and 5.23 × 1010 C/m3, respectively. Comparisons of the intensity tensor of aegirine–augite with those of aegirine and augite (Wo40En45Fs16) that have already been reported and the IXX, IYY, IXY and IZZ intensity tensor components of aegirine–augite in this study are almost the same as those of aegirine, but different from those of augite. While the M2 sites of aegirine–augite and aegirine are fully occupied with Na+ and Ca2+ ions, the M2 sites of augite are not fully occupied with Ca2+. The compositional dependency of the intensity tensor components suggests that the intensity tensor components for Fe3+ at the M1 site of a solid solution between aegirine and augite are dependent on the occupancy of large cations such as Ca2+ and Na+ at M2 sites.