Final answer:
Magma or lava cooling and solidifying causes the formation of igneous rock. Sedimentary rocks form through cementation of broken rock pieces, while metamorphic rocks are formed through the alteration of pre-existing rocks by heat and pressure.
Step-by-step explanation:
Igneous rocks form when magma or lava cools and solidifies. Minerals start to crystallize as the magma cools, and they interlock with each other in random orientations. Sedimentary rocks form when broken pieces of other rocks from weathering processes get cemented together. They can also form when minerals precipitate out of a solution, typically water, and are cemented together through sedimentary processes. Metamorphic rocks are pre-existing rocks that are altered by heat and pressure. Metamorphism often results in some type of pattern or orientation to the minerals, called foliation.