Amber, like many minerals, can be found in beach sand, because rivers erode the amber from the rocks that it was initially part of and wash it downstream until it arrives at the ocean. Alternatively, if there is rock containing amber near the ocean, the ocean waves themselves can erode the rock. Unlike most minerals, amber can float in seawater. This means that even if a river washes the amber out into the ocean, the waves can carry it back to the shore. That way, the amber accumulates on the beach.