Pc. Burnley et A. Navrotsky, SYNTHESIS OF HIGH-PRESSURE HYDROUS MAGNESIUM SILICATES - OBSERVATIONSAND ANALYSIS, The American mineralogist, 81(3-4), 1996, pp. 317-326
Specimens of dense high-pressure hydrous magnesium silicates, notably
phase A, phase B, and superhydrous phase B, have been synthesized for
use in calorimetric and spectroscopic experiments. X-ray diffraction a
nd electron microprobe analysis were used to study both major and mino
r phases occurring in the experimental products. We observed the forma
tion of phase A at 16 GPa, 1172 degrees C; phase B at 15 GPa, 1158 deg
rees C; chondrodite at 12 GPa, 1158 degrees C; and clinohumite at 12 G
Pa, 1170 degrees C. These pressures and temperatures are higher than t
hose reported in previous studies. We also observed the formation of p
hases E and superhydrous B at conditions at which they have been previ
ously observed. However, we propose that there is a high-low transitio
n in superhydrous B. We have not identified phase C in the pressure-te
mperature-bulk compositional space where it has been observed in previ
ous studies. We conclude that this phase may be identical with superhy
drous B, as previously suggested, or that in some studies a humite may
have been misidentified as phase C.