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.
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