Pressure-temperature studies of talc plus water using X-ray diffraction

X-ray diffraction measurements of natural talc plus water at combined pressures and temperatures of 0-15 GPa and 23-400 degrees C reveal the presence of a structural change that could be interpreted as a new high-pressure phase at 4.0 (+/- 0.5) GPa, and raise the possibility that the newly inferred phase transition takes place in cold subducting stabs as a precursor to appearance of the 10 angstrom phase of talc.