A rock is defined by geologists as a natural solid substance composed of one or more minerals fused together.

Rocks are not the same as minerals. Minerals are naturally occurring inorganic crystalline solids with a fixed chemical composition, while rocks are aggregates of minerals or sometimes mineraloids.

There are 3 main types of rocks: igneous, sedimentary, and metamorphic.

Igneous rocks form from molten magma or lava that cools and solidifies.

Sedimentary rocks are formed from layers of sediment, such as sand, mud, and small particles, which are compacted and cemented over time.

Metamorphic rocks originate when existing rocks are altered by heat, pressure, or chemically active fluids.

Rocks serve as a record of Earth’s history, as they can reveal past climates, tectonic events, and the evolution of life.

Many everyday structures and buildings rely on rock materials, such as stone, marble, and granite, which all originate from geological rock types.

Sedimentary rocks often preserve fossils because they form from layers that bury and protect the remains of plants and animals.

One of the most abundant igneous rocks is granite, and one of the most common volcanic igneous rocks is basalt.

Sandstone, shale, and limestone are common sedimentary rocks.

Slate and marble are examples of metamorphic rocks.

Many rocks we see at the surface were once deep beneath Earth’s crust and have been uplifted and exposed by erosion and tectonic forces.

Rocks can also be moved by surprising forces, such as the sailing stones in desert playas, where rocks move across flat surfaces and leave trails.

Some rocks, such as pumice, are so filled with holes, known as vesicles, that they can temporarily float on water.

Rocks also play a role in climate, since carbonate rocks like limestone can act as a sink for CO₂.