Scientists classify all the rocks in the world as igneous, sedimentary, or metamorphic. Igneous rocks form when magma cools slowly under the earth’s surface or rapidly when an active volcano throws it out.
People find these rocks beautiful and fascinating, but they also hold commercial importance for building materials, jewelry, fertilizers, and more, and they can reveal information about the geology of the Earth’s interior.
Igneous rock constitutes one of the three types of rock that make up the Earth’s crust (the other two are metamorphic and sedimentary rocks). The term comes from the Latin igneus meaning fiery, and solidified molten rock or lava composes igneous rocks.
Igneous rocks form when magma or lava cools, but different conditions can create different kinds of rocks. The two main types of igneous rocks are intrusive and extrusive.
Intrusive rocks form when magma cools and solidifies inside the Earth without reaching the surface. It cools slowly, allowing crystals to grow longer and become large chunks of mineral within the rock. Some of the more common intrusive rocks include granite, basalt and gabbro, or diorite.
Extrusive rock is a type of igneous rock that forms when magma reaches the Earth’s surface and becomes lava. Extrusive rocks can form in lava flows or in pyroclastic material that erupts into the air during a volcanic eruption. In either case, the lava cools too fast for large crystals to form, resulting in a fine-grained texture in the rock. Examples of these types of rocks include andesite, rhyolite, and many more.
Geologists find igneous rocks geologically important because their minerals and global chemistry provide information about the composition of the mantle, from which some igneous rocks extract, and the temperature and pressure conditions that facilitate this extraction, and/or of other pre-existing rock that melts.
Researchers can obtain their absolute ages from various forms of radiometric dating and thus compare them to adjacent geological strata, allowing for a time sequence of events.
Their features usually characterize a specific tectonic environment, enabling tectonic reconstitutions in certain special circumstances where they host important mineral deposits (ores): for example, tungsten, tin, and uranium commonly associate with granites and diorites, whereas ores of chromium and platinum commonly associate with gabbros.
Fun Facts About Igneous Rocks
Cooling magma under the earth’s surface or cooling lava near or on the earth’s surface forms igneous rocks.
Pumice, an igneous rock, can float on water because of gas pockets in its pores.
You may have igneous rocks in your house, as builders commonly use them for construction, interior design, decorative items, and jewelry.
Obsidian, a kind of volcanic glass, is sharper than a scalpel and served in ancient times to perform surgery.
Half Dome, the most famous feature of Yellowstone National Park, stands as a gigantic igneous rock.
Color serves as one of the means of classifying these rocks, but you must break the rock to see the interior color since weathering can affect the exterior.
