You can start a fire with ice.
Start by shaping an extremely clear piece of ice into a disc that is thick in the middle and narrow at the edges. Now, smooth away any rough edges with the warmth of your hands. Angle your ice lens towards the sun, focusing the light on a pile of tinder. The ice acts as a convex lens, directing photons to a localized point. The resulting concentration of heat energy can reach extremely high temperatures, allowing the tinder to catch on fire. This is sometimes easier said than done- the purity of the ice, thickness of the lens, and quality of tinder can all affect the process.