LENGTH SCALE DEPENDENCE OF HIGH-PRESSURE AMORPHIZATION - THE STATIC AMORPHIZATION OF ANORTHITE

High-pressure amorphization of anorthite has been observed by energy-d ispersive X-ray diffraction of powdered samples held under static pres sure in a diamond anvil cell. The onset of amorphization is accompanie d by a significant reduction in the intensity of Bragg reflections at pressures between 10 and 14 GPa, and anorthite becomes completely X-ra y amorphous between 14 and 20 GPa. These pressures are significantly l ower than those suggested by earlier birefringence studies. The discre pancy can be reconciled in terms of a model of high-pressure amorphiza tion in which partially amorphized anorthite can be regarded as a spat ially heterogeneous anti-glass, with long-range order maintained but t ranslational disorder dominating at shorter correlation lengths.