Abstract

A (Ca0.36Na0.56Mg0.08)(Mg0.73Si0.27)Si2O6 clinopyroxene containing both four- and six-coordinated silicon was synthesized at 15 GPa and 1600 °C and its structure determined with single-crystal X-ray diffraction. Unlike the Na(Mg0.5Si0.5)Si2O6 clinopyroxene that exhibits an ordered P2/n structure with octahedrally coordinated Mg2+ and Si4+ occupying two crystallographically distinct M1 sites (Angel et al. 1988), our sample possesses a C2/c symmetry and shows no detectable ordering between Mg2+ and Si4+ in the M1 site. The measured unit-cell parameters are a = 9.5792(13), b = 8.7588(12), c = 5.2610(6) Å, β = 107.199(3)°, and V = 421.7(2) Å3. The crystal structure of the clinopyroxene reported in this study is comparable to that for omphacites formed under high temperatures and pressures.

You do not currently have access to this article.