Equation of state of a new calcium magnesium silicate compound with the composition Ca3MgSi2O8 at pressures up to 23 GPa and ambient T

Interaction between the Ca-rich and Ca-poor (or Mg-rich) domains in the mantle may lead to formation of some special calcium magnesium silicates (CMS), as indicated by the unusual mineral inclusion with the chemical formula Ca 2.85 Mg 0.96 Fe 0.11 Si 2.04 O 8 enclosed in a super-deep diamond from Brazil. The equations of state (EoS) of these CMS compounds are thus important. With a diamond-anvil cell, here we performed in situ synchrotron X-ray diffraction experiments at high P (up to ~ 23 GPa) and ambient T to constrain the EoS of a new CMS compound with the composition Ca 3 MgSi 2 O 8 and the space group C 2/ c . The obtained P – V data were fitted to the third-order Birch–Murnaghan EoS, yielding an isothermal bulk modulus K T = 108(2) GPa, its first pressure derivative K T ′ = 4.0(3) and room- P volume V 0 = 658.0(4) Å 3 . If K T ′ is fixed as 4, then K T = 108(1) GPa and V 0 = 658.0(3) Å 3 . In addition, no phase transition has been observed for this new CMS compound in the investigated P interval.