Although these sandstone rocks began as a collection of individual grains of sand, the sand grains themselves had to come from somewhere and something else. Geologists theorize that the sand grains may have broken off a larger rock formed earlier by a volcanic eruption. Or they may have broken off older sandstone rocks. Because the Earth is so dynamic, rocks are always changing. Minerals that make up rocks are constantly moved and acted upon by the environment.
Environmental agents change one type of rock into an entirely new rock.
To gain an idea of how the rock cycle works, the world rock tour that began in Hawaii might end in east Greenland. Millions of years ago there, magma deep inside the Earth forced its way into another rock and solidified. This created an igneous rock. That new rock now makes up a mountain formation in Greenland. And the rock cycle continues today.