Synthesis of enstatite single crystals at high pressure

mm-sized crystals of enstatite were synthesized under H (sub 2) O-saturated conditions at 25 kbar in a piston-cylinder apparatus. The bulk starting composition corresponded to enstatite, silica and water in the respective proportions of 60, 20 and 20 wt.%. The most successful synthesis runs were heated above the liquidus (1400 degrees C), followed by a slow temperature ramp (6 degrees /h) down to 1100 degrees C. Enstatite was the only crystallising phase, having exclusively been in contact with a silica-rich fluid or melt during the whole run. Synthesis products were analysed by X-ray diffraction and electron microprobe. IR-spectroscopy revealed that the enstatite contains approximately 280 ppm H (sub 2) O.