Different Types of Rocks

There are three different types of rocks based on the way they form. Most of the time, they are very easy to tell apart. 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 do 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 under the Earth’s crust. There are two types of igneous rock, intrusive and extrusive. Intrusive igneous rock is crystallized below Earth’s surface, and the 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 colored and contains pyroxene and olivine, while granite contains mainly quartz.

The other igneous rock is called Extrusive igneous rocks, they erupt into the surface where they cool quickly and form small crystals. Sometimes they cool so quick they form amorphous glass. These rocks include basalt and obsidian. Basalt is a fine grained, dark colored extrusive igneous rock made mainly of plagioclase and pyroxene. Obsidian is also a dark colored extrusive rock that cools so fast no crystals form. Igneous rocks form at divergent boundaries, subduction zones, convergent boundaries, and hot spots. Igneous rocks compose most of the Earth’s continental crust and nearly all of the oceanic crust.

The second rock in the rock cycle is called Sedimentary rock. Sedimentary rocks form 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. Rocks that are apart of chemical sedimentary rocks are iron ore, flint, and limestone. The final sedimentary rock is the organic rock. It forms from the accumulation of plants or animal debris. Just like the chemical sedimentary rock, the organic sedimentary rock also has limestone. Unlike igneous rocks, sedimentary rocks are born cool, mostly underwater. They are arranged in layer of sandy or clay like materials. Some might preserve signs of life like fossils, tracks, or ripple. The main thing about sedimentary rocks is that they don’t change that much when they turn into rock.

The last and final class of rocks is the Metamorphic rock. They are formed when sedimentary and igneous rocks become metamorphosed underground. The main things that make metamorphose rocks are heat, pressure, fluids, and strain. All metamorphic rocks are formed by great heat and pressure. They are almost always strong rocks, made of different minerals, have a wide range of color and luster, and have a striped appearance. Foliated metamorphic rocks are caused when there is high pressure and heat. Rocks that form under these conditions are called schist or gneiss. Non-foliated rocks occur when the is low pressure but high heat. In conclusion all three rocks are important. They all come from the same cycle, the rock cycle, but are all different in their own ways. You can tell the difference between all of them because of their very different characteristics.

Works Cited

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