HIGH-PRESSURE PHASE-TRANSFORMATIONS IN MGF2 (RUTILE)

Employing a diamond‐anvil pressure cell and a YAG laser as a heating source, phase relationships in polycrystalline MgF2 (rutile) were investigated to ∼330 kbar at both room temperature (∼23°C), and high temperature (∼1300°C). In situ high pressure X‐ray diffraction data show that MgF2 (I) of rutile structure transforms into MgF2(II) of a cubic structure at ∼300 kbar at room temperature, and at ∼190 kbar at high temperature (∼1300°C), resulting in a negative dP/dT slope for the univariant line between MgF2(I) and MgF2(II) in the P‐T phase diagram. The molar volume differences at room temperature between MgF2(I) and MgF2(II) at 190 kbar and 300 kbar are ∼8% and ∼5%, respectively. © 1979 by the Chinese Geophysical Society