Sedimentary rocks - layers of rock fragments that were compressed and cemented together.They often contain fossils.
Igneous rocks - molten rock that cools and solidifies.They do not contain fossils.
Metamorphic rocks - existing rocks that are compressed and heated without melting.They have the same chemical composition as the rocks from which they were made.
sedimentary rocks 和 igneous rocks 和 metamorphic rocks是三中最基本的石头,the rock cycle 就是这三种石头的循环