Influence of Hydrogen and Alkali Impurities on the High‐Temperature Indentation Hardness of Natural Quartz Crystals

Abstract

The indentation hardness of a natural quartz crystal was measured from 25° to 1000°C. The concentrations of alkali ions and hydrogen were varied by annealing and electrolysis; hydrogen content was determined from infrared absorption. The untreated crystal was soft from 500° to 850°C; there was evidence of transformation beneath the indenter to a phase of silica denser than quartz. When the crystal was annealed to remove alkali ions and hydrogen, it remained hard throughout the temperature range of the tests. Injection of hydrogen by electrolysis into previously annealed specimens reduced the strength slightly; injection of lithium by electrolysis produced a greater reduction in hardness. Only the untreated samples and those doped with lithium appeared to have transformed to a denser phase. Thus, trace impurities can influence the hardness of quartz by acting as “mineralizers” to promote densification and by facilitating normal deformation mechanisms involving dislocations.