The equation of state for ¿-Fe2SiO4 was determined by single-crystal X-ray diffraction up to 10.2 GPa at room temperature. The pressure–volume data, measured at 10 different pressures, do not show any evidence of a phase transformation and were fit by a third-order Birch–Murnaghan equation of state. The following coefficients were refined simultaneously: V₀ = 559.44(6) ų, K_T0 = 187.3(1.7) GPa, and K' = 5.5(4).
This result implies that the Mg/Fe substitution along the ¿-Fo–Fa join does not significantly affect the bulk modulus. The sample shows higher K' than other compositions along the Fo–Fa join, which generally have K' ~4. Based on our results we can calculate the sound bulk velocity of ¿-Fe2SiO4 up to the pressures of the Transition Zone. Due to the larger K' of ¿-Fe2SiO4, the difference in bulk sound velocity between the two end-members decreases with increasing pressure.