You can explode large stones in the winter quite easily.Look for a flint that is well frozen through and pour boiling water over it. It breaks apart with cracks and bangs. The explosive effect is caused by the outer layers heating and expanding faster than the centre. The resulting tension causes the stone to burst. In the same way thick walled glasses may explode if you pour hot liquids into them. Glass conducts heat poorly, so that the layers of glass expand by different amounts.