Abstract
The stability region of chrysotile in the system MgO-SiO2-H2O has previously been investigated by Bowen and Tuttle, showing that chrysotile can be prepared at temperatures below 500°C, and at water vapor pressures from 2, 000 to 40, 000lb/in2 and break down into forsterite, talc and water vapor under hydrothermal conditions above 500°C. But the treated pressures were much lower, as described above.
This research was carried out as a part of the study on the synthesis of fluor-chrysotile [Mg6Si4O10(F)8]. Mixtures of SiO2 (amorphous) and Mg(OH)2 (brucite) specimens corresponding to chrysotile composition, and natural chrysotile were treated at temperatures ranging from 300° to 600°C and pressures from 2 to 40 kb using a simple squeezer type high pressure apparatus. The present experimental results have indicated that chrysotile can not be formed at 10kb and temperatures above 510°C, at 20kb above 530°C.
The pressure-temperature curve of the equilibrium, chrysotile _??_ talc+forsterite+water vapor, was appeared to be lying on the extrapolated line of Bowen and Tuttle's pressure-temperature curve. The value of (∂P/∂T) was about 8.0×102(bar/deg.) and was in good agreement with that calculated by thermodynamic data. The synthesized chrysotile crystal was always appeared as minute tubular, not platy and fibrous by photographs in the electron microscope and had the low refractive indices of chrysotile.
