Comparison of the effective heat conductivity of a binary mixture of olivine and nickel-iron determined from a solution of the heat conduction equation and compared with predictions of different mixing rules. Crosses: Effective heat conductivity determined from the numerical solution with n = 100 (black) and n = 200 (red). The multiple crosses at a volume fraction of 0.2, 0.5, and 0.8, shifted by 3 upwards, correspond to results calculated for different realisations of the random distribution of the mixture components. Long-dashed lines: theoretical upper and lower limits for heat conductivity of the mixture given by Eqs. (15) and (16), respectively. Short dashed line: geometric mean according to Eq. (13). Solid line: Effective heat conductivity according to the Bruggeman effective medium theory, given by Eq. (17).