That's a rock. It bounces back because the minerals in rocks are glued, or cemented, together. You can usually dig into it with a pick or shovel. Most of these deposits are not cemented together. Unconsolidated sediments, if they occur in an area, exist to the surface of the rocks.
Many different materials can exist in the voids in rocks and unconsolidated sediments.
Some of them are solids like tiny flecks of gold, some are liquids like oil or ground water, and some are gases like the natural gas we burn to heat our homes.