The phase boundary between α- and β-Mg₂SiO ₄ determined by in situ x-ray observation

The stability of Mg₂SiO₄, a major constituent in the Earth's mantle, has been investigated experimentally by in situ observation with synchrotron radiation. A cubic-type high-pressure apparatus equipped with sintered diamond anvils has been used over pressures of 11 to 15 gigapascals and temperatures of 800° to 1600°C. The phase stability of α-Mg ₂SiO₄ and β-Mg₂SiO₄ was determined by taking account of the kinetic behavior of transition. The phase boundary between α-Mg₂SiO₄ and β-Mg ₂SiO₄ is approximated by the linear expression P = (9.3 ± 0.1) + (0.0036 ± 0.0002)T, where P is pressure in gigapascals and T is temperature in degrees Celsius.