There are three different types of rocks based on how they form. Most of the time they are very easy to distinguish. These three 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 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. The intrusive igneous rock is crystallized 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 Should Not Be Banned”? Get the original essay The other igneous rock is called extrusive igneous rocks, they burst to the surface where they cool quickly and form small crystals. Sometimes they cool so quickly that they form 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 no crystals form. Igneous rocks form at divergent boundaries, subduction zones, convergent boundaries, and hotspots. Igneous rocks make up most of Earth's continental crust and almost all of oceanic crust. The second rock in the rock cycle is called sedimentary rock. Sedimentary rocks are formed by accumulation of sediment. There are three types of sedimentary rocks, namely clastic, chemical and organic sedimentary rocks. Clastic sedimentary rocks are formed from debris from mechanical weathering. Examples of clastic rocks are sandstone and breccia. The second sedimentary rock is called chemical sedimentary rock. They form when dissolved materials precipitate from solution. Rocks that are part of chemical sedimentary rocks are iron ore, flint and limestone. The final sedimentary rock is organic rock. It forms 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 cold, mainly underwater. They are arranged in layers of sandy or clayey materials. Some may retain signs of life such as fossils, traces or ripples. The main thing about sedimentary rocks is that they don't change much when they turn into rock. Keep in mind: this is just a sample. Get a personalized article from our expert writers now. Get a Custom Essay The last and final class of rocks is metamorphic rock. They form when sedimentary and igneous rocks metamorphose underground. The main elements that cause rocks to metamorphose are heat, pressure, fluids and deformation. All metamorphic rocks are formed by significant heat and pressure. They are almost always solid rocks, made of different minerals, which have a wide range of colors and luster and have a striped appearance. Metamorphic rocks.