Rocks are grouped into three types.  These are igneous, sedimentary and matamorphic rocks.

Igneous rocks are solid rocks that formed from magma or molten rocks.

Sedimentary rocks are formed from sedimentation, or when igneous rocks are eroded as a sediment under the sea. These include limestone, iron ore, chalk, rock salt and sandstone.

Metamorphic rocks began as igneous or sedimentary rocks which have changed in form because of intense heat or pressure. These include slate, marble, and quartzite.