Our planet is mostly made of solid rock. Rock is what gives Earth its features - mountains, canyons, and plains. Minerals are the building blocks of every type of rock.
Most of Earth's rocks are hidden under a layer of soil and vegetation, but in some places they are visible at the surface, in landscape features such as mountains and canyons. Many different types of rock have developed over billions of years, through a variety of processes. These include volcanic activity, which creates rocks at or near the surface, the formation of sediments in places like the seafloor, and changes in form - called metamorphism - brought about by heat and pressure deep within our planet. These processes are linked in a never-ending cycle, known as the rock cycle.
A rock is a hard natural object made of mineral grains (crystals), held together in a compact structure. There are hundreds of different kinds of rock, but they are grouped into three main types - igneous, sedimentary, and metamorphic - depending on how they were formed.
Igneous: These form when hot liquid rock, called magma or lava, cools down and solidifies.
Sedimentary: These form when particles from other, older rocks are compressed and stick together.
Metamorphic: These rocks form when older rocks are changed by heat and pressure.
Rocks transform from one type into another in an endless cycle. Many factors contribute to this process, both on the Earth’s surface and in its interior. On the surface, rock is broken down by weathering, and glaciers, rivers, and winds erode rocks by carrying particles of them away. Sediment made of tiny particles of rock and mud forms in places like lake bottoms, coasts, and seabeds.
Inside the Earth, heat, pressure, and melting change sedimentary and igneous rock into metamorphic rock, and volcanoes are formed that create new igneous rock.
Rocks are made up of minerals. There are thousands of minerals, but only around 30 are found at Earth's surface. Most minerals are crystals - their atoms are arranged in regular patterns, giving them simple geometric shapes. Each mineral has its own chemical composition and physical properties.
Native elements: These minerals each contain a single chemical element, such as sulfur, carbon, or a metal such as copper.
Compounds: These minerals contain two or more chemical elements. For example, Fluorite contains calcium and fluorine.