Microstructures in water-weakened single crystals of quartz

Models of hydrolytic weakening based on the influence of chemical environment on the concentrations of point defects stimulated a series of experiments by Ord and Hobbs [1986] in which single crystals of natural quartz were deformed in a solid medium apparatus under a range of buffered oxygen, water, and hydrogen fugacities. Microstructures in these specimens have been examined using visible light and transmission electron microscopy in an attempt to identify processes responsible for the observed relationships between chemical environment and strength. It is inferred from the dependence of the degree of fracturing upon chemical environment, together with a high correlation between locations of plastic strain and regions of earlier fracture, that the relationship between chemical environment and macroscopic strength of natural quartz crystal is not simply a matter of water weakening as a direct result of high point defect concentrations. Instead, fracture, inferred to be important in natural fluid-rock interactions, also seems to be an experimentally critical process which might nucleate the dislocations necessary to initiate plastic deformation in the laboratory. -from Authors