SYSTEM ENSTATITE-WOLLASTONITE AT HIGH-PRESSURES AND TEMPERATURES, WITH EMPHASIS ON DIOPSIDE

High-pressure phase transformations for three intermediate compositions (including diopside) in the system enstatite (MgSiO3)-wollastonite (CaSiO3) were investigated in the pressure range 100-300 kbar at about 1000°C in a diamond-anvil press coupled with laser heating. The phase behaviour of the two end components (enstatite and wollastonite) at high pressure has been reported earlier. The results of this study reveal that there is very limited solid solution of diopside (CaMgSi2O6) in the various high-pressure phase assemblages of enstatite. At pressures greater than about 200 kbar, diopside and a composition between diopside and wollastonite were found to transform into non-quenchable phases, as does wollastonite. It is thought probable that diopside and wollastonite form solid solutions with the perovskite structure at high pressure, but that on release of pressure it is not possible to preserve the high-pressure modification. © 1979.