The effect of iron on the P21lc to C2/c transition in (Mg,Fe)SiO3 clinopyroxenes
Ross, Nancy L.; Reynard, Bruno
European Journal of Mineralogy Volume 11 Number 3 (1999), p. 585 - 590
published: May 25, 1999
manuscript accepted: Jan 29, 1999
manuscript received: Aug 16, 1998
ArtNo. ESP147051103016, Price: 29.00 €
Abstract High-pressure Raman spectroscopy has been used to investigate the effect of iron on the low-clinoenstatite (space group P21/c) to high-density clinoenstatite (space group C2lc) transition for clinopyroxenes along the MgSiO3-FeSiO3 join. For the MgSiO3 endmember, the transition to the C2/c structure occurs at 7.89 GPa upon increasing pressure and reverts to P21/c symmetry at 4.59 GPa upon decreasing pressure. Both the transition pressure and the hysteresis of the transition decreases markedly with addition of iron. The transition has been bracketed between 0.5 GPa or less for compositions with XFe ≥ 30 %. The variation of the transition pressure with increasing iron content can be described by the following equation: Pt (GPa) = (5.97 ± 0.14) - (4.26 ± 0.23) XFe. The decrease in transition pressure and the hysteresis of the P21lc to C2/c transition observed in Fe-bearing clinopyroxenes may be due, in part, to crystal field stabilization energy arising from iron in the octahedral sites of the C2lc structure.