History of Earth
Rocks come in many sizes, colors, and shapes.
The classification depends upon how the rock was formed.
Igneous rocks are formed from melted rock. The word, "igneous", is similar to "ignite" (which means to start a fire).
Sedimentary rocks are formed from sediments, stuff that settles down. Remember that sediment settles.
Metamorphic rocks form from existing rocks that have been exposed to extreme pressure and temperature deep inside the Earth.