Silica phases and the effects of phase transformation on electrical conductivity – just another mineral to test or a major player in the Earth's field?

Silica has many distinct polymorphs, however those most widely applicable to understanding the Earth are alpha quartz, coesite and stishovite. While a large amount of high pressure electrical conductivity work has been done on alpha quartz (Wang et al., 2012) no measurements have been done on the beta-quartz or coesite phases and only one work has been able to generate a measurement of stishovite (Yoshino et al., 2014). The work presented here has looked to begin filling in these knowledge gaps by undertaking measurements at 1, 6 and 8.7 GPa with the intention to generate measurements of alpha quartz, coesite and stishovite, respectively. Electrical conductivity measurements were obtained at 100K intervals within the temperature range 373–1273 K and the enthalpy of each polymorph was calculated. Therefore, in this abstract we present the first Electrical conductivity measurements on coesite accompanied by new measurements on alpha quartz including FTIR data on water contents and Raman data on phase. The resulting electrical conductivity values are modelled over a magnetotelluric profile obtained through the tectonically stable Northern Australian Craton. Given their relative abundances, these results imply potentially high electrical conductivities in the crust and mantle from contributions of silica polymorphs