Sedimentary rock is like a sandwich filled with many different layers. It forms in layers and hardens from high temperature and pressure. Another type of rock is metamorphic. It changes into different rock from heat and pressure. Metamorphic rock is like melting an Oreo and then letting it harden.
Marble is a metamorphic rock.
The last kind of rock type is igneous. Igneous rocks are made from lava that hardens. Igneous rocks are like glue that comes out of a tube and hardens. Rocks and minerals are very old. There are a lot of rocks and minerals in the world.