The snow melts faster on some cobblestones in front of our house than on others. Using a Geiger-Mueller counter, I was able to disprove the explanation of a friend, who claimed that these cobblestones were warmer due to being radioactive.
I found experimentally that the snow melts faster on cobblestones that have a higher thermal conductivity, as they transport heat from the warmer soil to the surface more effectively than other cobblestones. The heat capacity of the stones is not of major importance.