How does intrusive igneous rock reach the surface

A82Unit:Earth’s SurfaceVOCABULARYintrusive igneous rock p. 83extrusive igneous rock p. 83BEFORE, you learned•Earth’s interior is very hot•Most minerals in Earth’s crustare silicatesNOW, you will learn•Why igneous rocks formed atEarth’s surface are differentfrom those formed within Earth•Why silica content is importantin classifying igneous rocks•Why igneous rocks can makelong-lasting landformsKEY CONCEPTIgneous rocks form from molten rock.THINK ABOUTWhy do two rocks made of the same mineralslook very different?Look at a sample of granite and a sample of rhyolite (RY-uh-LY T).These two igneous rocks contain the same minerals, so their chemicalcompositions are very similar.Yet granite and rhyolite look very different. What do you think might cause this difference?Magma and lava form different types ofigneous rocks.Igneous rocks form from molten rock, but where does molten rockcome from? The temperature inside Earth increases with depth.That is, the farther down you go, the hotter it gets. Deep within Earth,temperatures are hot enough—750°C to 1250°C (about 1400°F to2300°F)—to melt rock. This molten rock is called magma. Molten rock that reaches Earth’s surface is called lava.Anigneous rock is classified on the basis of its mineral compositionand the size of its mineral crystals. A rock formed from magma canhave the same composition as a rock formed from lava. The rocks,though, will have different names, because the sizes of their crystalswill be very different. You will read why later in this section.People’s decisions about how to use igneous rocks are based inpart on the rocks’ crystal sizes. For example, rocks with large mineralcrystals are often used as building stones because they are attractive.MAIN IDEA WEBRemember to make aweb for each main idea.graniterhyolite

Chapter 3:Rocks83Origin of Igneous RocksDepending on where they form, igneous rocks are classified as intrusive (ihn-TROO-sihv) or extrusive (ihk-STROO-sihv).Anis one that forms when magma coolswithin Earth. An is one that forms when lava cools on Earth’s surface.Granite is a common intrusive rock in continents. If magma withthe same composition reaches the surface, it forms extrusive rockssuch as rhyolite and pumice (PUHM-ihs). Basalt (buh-SAWLT) is anextrusive igneous rock that forms the ocean floor. Gabbro is an intru-sive rock that has the same composition as basalt.check your readingHow are gabbro and basalt similar? How are they different?You can see extrusive igneous rocks at Earth’s surface. But intrusiveigneous rocks form within Earth. How do they reach the surface?Forces inside Earth can push rocks up, as when mountains form.Also, water and wind break apart and carry away surface rocks.Then deeper rocks are uncovered at the surface.extrusive igneous rockintrusive igneous rockVOCABULARYAdd magnet word diagrams for intrusiveigneous rockand extrusive igneous rockto your notebook.ExtrusiveMolten rock that cools onEarth’s surface forms extrusiveigneous rocks. Examples are rhyolite, pumice, and basalt.Types of Igneous RocksIntrusiveMolten rock that cools withinEarth forms intrusive igneousrocks. Examples are granite and gabbro.basaltgabbrograniterhyolitepumiceIs the volcano in the illustration built of layers of intrusive or extrusive igneous rock? Explain your answer.A