QUARTZ PREFERRED ORIENTATION AND ITS IMPACT ON THERMAL ANISOTROPY IN SANDSTONE AND QUARTZITE

Thermal conductivity may be defined as the rate of heat transfer through a material. Many crystalline materials display variable thermal conductivity as a function of crystal orientation; such materials are referred to as thermally anisotropic. Quartz, one of the most abundant minerals in the Earth’s crust, is one such mineral. Therefore, the thermal conductivity of quartzite, a rock defined as having >95% quartz, should vary as a function of quartz crystal preferred orientation. If the preferred orientation of quartz in quartzite can be measured, it should be possible to model the thermal properties of the rock and estimate its potential as a latent heat-source for geothermal energy production.

Quartzites with varying preferred grain orientation were sampled along two traverses in central New Mexico. Quartz grain orientation was measured using Electron Back Scatter Diffraction (EBSD). In one traverse, increasing quartz preferred orientation was measured with increasing proximity to a crustal-scale deformation-shear zone. In the second traverse, an increase in crystal preferred orientation was observed with increasing proximity to a large granite intrusion. Using the thermal properties of quartz and the measured quartz preferred orientation, calculations show that the thermal conductivity of the samples should increase with proximity to the shear-zone and the granite intrusion.

An experimental apparatus that measures the variation of temperature versus time in a sample in response to the input of thermal energy will be used to collect data from which actual thermal conductivity values will be calculated. If measured thermal conductivity of quartzite does vary as a function of measured quartz preferred orientation, the results may provide the basis of a model for identifying potential sites for passive geothermal energy plants.