The Hydrolytic Weakening Effect in Quartz

  1. Robert N. Schock
  1. B. E. Hobbs

Published Online: 18 MAR 2013

DOI: 10.1029/GM031p0151

Point Defects in Minerals

Point Defects in Minerals

How to Cite

Hobbs, B. E. (1985) The Hydrolytic Weakening Effect in Quartz, in Point Defects in Minerals (ed R. N. Schock), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM031p0151

Author Information

  1. Department of Earth Sciences, Monash University, Clayton, Victoria 3168, Australia

Publication History

  1. Published Online: 18 MAR 2013
  2. Published Print: 1 JAN 1985

ISBN Information

Print ISBN: 9780875900568

Online ISBN: 9781118664070



  • Mineralogical chemistry—Congresses;
  • Crystals—Defects—Congresses


Experiments on single crystals of quartz have shown that an order of magnitude increase in the fugacity of H2O is associated with about an order of magnitude decrease in the flow strength at a given temperature and pressure. The classical interpretation of this hydrolytic weakening effect is that H2O groups are incorporated into the quartz structure as Si-OH.HO-Si groups. Then, in order to move a dislocation, OH.HO bonds need to be broken rather than Si-O bonds. The rate controlling process is envisaged as the diffusion of the (OH)-defect to or with the dislocation core. This paper discusses the manner in which charged hydrogen- or hydroxyl-defects alter the concentrations of other charged defects such as kinks and jogs on dislocations or vacancies and interstitials and so have an influence on the deformation rate. As an example, an increase in the concentration of negatively charged (OH)-defects leads to an increase in the concentration of positively charged kinks on dislocations thus increasing the strain rate. Other deformation mechanisms involving diffusion of oxygen and silicon with or without climb of dislocations or motion of kinks are also investigated and are shown to be capable of explaining the observed effect. This defect chemistry interpretation is consistent with the classical interpretation but also proposes other mechanisms where the direct diffusion of (OH)-defects plays no role in the process. As an example, an increase in the concentration of negatively charged (OH)-defects increases both the concentration of positively charged jogs and positively charged silicon interstitials in such a way as to explain the magnitude of the hydrolytic weakening effect. As such, the rate controlling process is the climb of dislocations controlled by silicon diffusion, not the diffusion of (OH)-defects. Although several different mechanisms are capable of explaining the hydrolytic weakening effect, many have different dependencies upon the activity of oxygen so that properly designed experiments are capable of establishing which mechanism actually operates.