Structure of (FexCa1-xO)(y)(SiO2)(1-y) liquids and glasses from high-energy x-ray diffraction: Implications for the structure of natural basaltic magmas

The atomistic structure of (FexCa1-xO)(y) (SiO2)(1-y) liquids, namely, fayalite (x = 1, y = 0.667), ferrosilite (x = 1, y = 0.5), and hedenbergite (x = 0.5, y = 0.5), was measured by using high-energy x-ray diffraction combined with laser-heated aerodynamic levitation. Measurements were also made for hedenbergite glass, formed via supercooling the liquid. The results unequivocally prove that Fe atoms are both four and sixfold coordinated by oxygen atoms in all compositions studied from the two distinct bond distances measured at r(FeO) = 1.93 and 2.20 angstrom, respectively. The results quantitatively reveal up to 40% and 55% FeO6 species residing in liquid fayalite and ferrosilite, respectively. From the real-space peak positions, the results also reveal the presence of both FeO4 and FeO6 species within a basaltic liquid and glass for which the geophysical consequences are briefly discussed.