Rocks are categorized into three types: igneous, sedimentary and metamorphic. They are mainly classified based on the processes they undergo during formation.
Rocks are one of the most predominant physical features found on Earth. They are generally composed of minerals, which are subjected to certain geological conditions that influence the properties they acquire during formation.
Igneous rocks are formed through the cooling and solidification of hot molten material called magma, either beneath or on the surface of the earth. Rapid cooling results in smooth-grained, glass-like textures, while slow cooling leads to the formation of large crystals and coarse-grained consistencies. The colors vary from white and pink in granite to grey and dark black in porphyrite and obsidian. Basalt is the most common type of igneous rock.
Sedimentary rocks are formed through the deposition of particle materials known as sediments, such as sand, pebbles and small pieces of organic matter. These rocks form in layers by undergoing lithification and cementation processes. Most sedimentary rocks are light to dark brown in coloration, fine-grained, easily crumble and typically contain fossilized remains. Common examples of sedimentary rocks include shale, limestone, conglomerate and chalk.
Metamorphic rocks develop through the exposure of igneous or sedimentary rocks to intense temperatures and pressure. The minerals become more condensed and the structure of igneous and sedimentary rocks is transformed into a more compact form. Colors can range from gray to green in slate and dark in gneiss and schist. Some are fine-grained, while others exhibit prominent crystallization.