Hydrothermal experiments have been carried out to find the equilibrium conditions for the reactions:
2kaolinite=pyrophyllite+2diaspore+2water (1)
kaolinite+2quartz=pyrophyllite+water (2) As starting materials, a natural mixture of kaolinite-pyrophyllite-boehmite was used for the experiments. Determination of reaction direction was based upon X-ray diffraction patterns.
It has been confirmed that the equilibrium curve for the reaction (1) passes through the points 325 ± 10°C at 1kb and 330 ± 10°C at 2kb, and the curve for the reaction (2) passes through 250 ± 10°C at 1kb and 260 ± 10°C at 2kb. The present temperatures for the reaction (2) are lower than any other one reported so far.