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[1] In situ X-ray diffraction measurements have been made on KAlSi 3 O 8 hollandite using diamond anvil cell and multianvil apparatus combined with synchrotron radiation. Both of the measurements with different techniques demonstrated that K-hollandite transforms to a new highpressure phase (hollandite II) at $22 GPa upon increasing pressure at room temperature. The X-ray diffraction peaks of the new phase were reasonably indexed on the basis of a monoclinic cell with I2/m space group. Hollandite II was also confirmed to be formed at high temperatures to 1200°C and pressures to 35 GPa, which was quenched to room temperature under pressure but converted back to hollandite at about 20 GPa on release of pressure. The present result is contradictory to earlier studies based mainly on quench method, which concluded that hollandite is stable up to 95 GPa at both room temperature and high temperatures up to 2300°C.

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The phase transition between CaSiO3 perovskite and Ca2SiO4 larnite + CaSi2O5 titanite has been investigated using a Kawai‐type multianvil apparatus (KMA) combined with synchrotron radiation. This phase boundary is located by our experiments as P (GPa) = 9.8(4) + 0.0017(3) × T (°C), which is 2–4 GPa lower than the most recent results using laser heated diamond anvil cell and those based on thermodynamic calculations, but is consistent with earlier studies based on quench experiments using KMA. The present results suggest some diamond inclusions recently found in Kankan distinct, Guinea, may originate from depth of 240–360 km in the upper mantle.