To determine the elastic modulus of polycrystalline mica with randomly oriented grains, the Voigt and Reuss averages should be calculated based on the given moduli of 52 GPa parallel to the c-axis and 179 GPa perpendicular to the c-axis. These averages provide upper and lower bounds for the actual elastic modulus of the material. The Voigt average assumes uniform strain, while the Reuss average assumes uniform stress. The calculations for these averages can be found in relevant literature, such as the linked book resource. This approach will yield a more accurate representation of the elastic properties of polycrystalline mica.
