The solid Earth is made of rock. A rock is a naturally occurring aggregate of minerals or mineral-like matter. Rocks are classified into three great groups according to origin: igneous, sedimentary, and metamorphic.

Igneous rocks crystallize from magma or lava. Sedimentary rocks form by accumulation and lithification of sediment or by chemical precipitation. Metamorphic rocks result from the solid-state transformation of existing rocks under heat and pressure. Each group contains many specific rock types defined by composition and texture.

Rocks record the processes that formed them and the conditions they later experienced. They are the source of most mineral and energy resources and the foundation of landscapes. The rock cycle links the three groups through geologic processes that operate over millions of years.

• Natural aggregate of minerals or mineraloids
• Classified as igneous, sedimentary, or metamorphic
• Records geologic processes and history
• Source of resources and foundation of landscapes