Rapid dissolution of minerals at microasperities in super-critical and sub-critical H2O

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Indentation tests (point-contact deformation) were performed using a nano-indentation tester with a load of 300 mN on a specimen of single crystal of quartz, and then the specimen was immersed in the sub-critical H2O generated in a pressure vessel at high temperature and pressure (350 deg C, 20 MPa) for two hours. We observed the indentation area of the specimen after the removal from the sub-critical H2O with a Laser microscope, and noticed that quartz in the indentation rapidly dissolved whereas intact quartz far from the indentation did not appreciably dissolved. We measured the dissolved volume of quartz and revealed a linear relationship between log(depth of indentation) and log(volume of resolved quartz). We also examined the influence of crystallographic orientation of quartz on the relationship between the depth of indentation and the energy required to produce the indentation, and concluded that crystallographic orientation has no influence on the relationship.