Abstract
High temperature impedance spectra, up to 450 °C, were measured for a microcrystalline quartz aggregate (chalcedony), which initially contained 0.3 wt% of liquid-like water (H2O) dispersed in grain boundaries and fluid inclusions together with 0.3 wt% of hydroxyl (Si-OH) in the crystal structure. Infrared spectra obtained after heating, showed dominant dehydration of liquid-like water, while much hydroxyl remained stable. Electrical conductivities before (wet) and after heating to 450 °C (dry) gave linear Arrhenius relations with apparent activation energies of 11 ± 1 kJ/mol for initial heating of the wet sample versus 32 ± 3 kJ/mol for the subsequently dry sample. Compared with previously reported Arrhenius relations for α-quartz single crystals, our activation energies are much lower, and the absolute conductivities we obtained range from similar values to three orders of magnitude higher. We infer that the presence of grain boundaries and/or triple junctions containing liquid-like water greatly influences the electrical conductivity.
