There are three different types of rocks based on how they are formed. In most cases it is very easy to distinguish them. All three of these rocks come from the rock cycle. These rocks are called igneous, metamorphic and sedimentary rocks. These rocks are all very different in many ways, but they have one thing in common: they are all made up of minerals. Igneous rocks are formed by the cooling and crystallization of magma. Magma is generated in the plastic asthenosphere, a layer of molten rock beneath the Earth's crust. There are two types of igneous rocks, intrusive and extrusive. Intrusive igneous rock crystallizes beneath the Earth's surface, and slow cooling causes large crystals to form. Examples of intrusive igneous rocks are gabbro and granite. Gabbro and granite are very similar but gabbro is dark in color and contains pyroxene and olivine, while granite contains mainly quartz. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay The other igneous rock is called extrusive igneous rocks, they erupt to the surface where they cool rapidly and form small crystals. Sometimes they cool so quickly that they form an amorphous glass. These rocks include basalt and obsidian. Basalt is a fine-grained, dark-colored, extrusive igneous rock composed primarily of plagioclase and pyroxene. Obsidian is also a dark-colored extrusive rock that cools so quickly that it does not form crystals. Igneous rocks form at divergent boundaries, subduction zones, convergent boundaries, and hot spots. Igneous rocks make up most of Earth's continental crust and nearly all of oceanic crust. The second rock in the rock cycle is called sedimentary rock. Sedimentary rocks are formed by the accumulation of sediments. There are three types of sedimentary rocks, which include clastic, chemical, and organic sedimentary rocks. Clastic sedimentary rocks are formed from mechanical weathering debris. Examples of clastic rocks are sandstone and breccia. The second sedimentary rock is called chemical sedimentary rocks. They form when dissolved materials precipitate from solution. The rocks that are part of the chemical sedimentary rocks are iron ore, flint and limestone. The final sedimentary rock is organic rock. It is formed from the accumulation of plant or animal debris. Just like chemical sedimentary rock, organic sedimentary rock also contains limestone. Unlike igneous rocks, sedimentary rocks are born fresh, mostly underwater. They are arranged in layers of sandy or clayey materials. Some may preserve signs of life such as fossils, tracks or ripples. The main thing about sedimentary rocks is that they don't change much when they turn into rock. Please note: this is just an example. Get a custom paper from our expert writers now. Get a Custom Essay The last and final class of rocks is the metamorphic rock. They form when sedimentary and igneous rocks undergo metamorphosis underground. The main elements that determine the metamorphosis of rocks are heat, pressure, fluids and tension. All metamorphic rocks are formed by great heat and pressure. They are almost always strong rocks, made up of different minerals, have a wide range of colors and luster, and have a striated appearance. Foliated metamorphic rocks form when there is high pressure and heat. Rocks that form under these conditions are called schist or gneiss. Non-foliated rocks form when pressure is low but heat is high. In conclusion all three rocks are important. They all come from the same cycle, the rock cycle,.