The main difference between igneous sedimentary and metamorphic rocks is that igneous rocks form from magma or lava and sedimentary rocks form from accumulation or deposition of small particles whereas metamorphic rocks form from the transformation of an existing rock type into a new form. Rocks are hard solid materials that occur on Earth – beneath the surface and above the surface. Basically, there are three major types of rocks classified based on the method of formation; igneous, sedimentary and metamorphic rocks. Key Areas Covered1. What are Igneous Rocks Key TermsIgneous Rocks, Sedimentary Rocks, Metamorphic Rocks  What are Igneous RocksIgneous rocks are a type of rocks that form due to the solidification of lava or magma. Therefore, these are also called magmatic rocks. These rocks form via solidification followed by cooling of lava or magma. Generally, magma forms from the partial melting of rocks that lies in either the mantle of Earth or its crust. There are basically three major processes that cause the melting of these rocks: increased temperature, decreased pressure, or changes in composition. The solidification of this magma into igneous rocks can happen either beneath the surface of Earth or on the top of the surface. Moreover, if this solidification occurs below the surface, we call it intrusive igneous rocks, and if it occurs on the surface, we call it an extrusive rock. Figure 1: Igneous Rock Igneous rocks may form via crystallization. This forms granular, crystalline rocks. But sometimes, these rocks form without crystallization. Then the rocks formed are known as natural glasses. We can observe the occurrence of igneous rocks at a wide range of landforms such as shields, platforms, orogens, basins, extended crusts, ocean crusts, etc. Generally, metamorphic and igneous rocks cover about 90% of the surface of the Earth’s crust. Moreover, most of the oceanic crusts on Earth are made of igneous rocks. What are Sedimentary RocksSedimentary rocks are a type of rocks that form via accumulation or deposition of sediment materials. This formation involves the deposition or accumulation followed by cementation with minerals or organic matter. These rocks form on the surface of the Earth. The process is called “sedimentation”. Figure 2: Sedimentary Rock Furthermore, rocks that form from sedimentation are “sediments”. The minerals for the cementation process are carried to a particular location by water, wind, ice, or mass movement. Organic matter for cementation is carried to the location via water flow in the form of piles. In addition, small scale sedimentation may occur due to the precipitation of sediment materials from water solution. Moreover, the coverage on the Earth surface with sedimentary rocks lies between 10-8% by volume. Metamorphic rocks are a type of rocks that form from the transformation of an existing rock type into a new rock type. We call this process metamorphism. We call the original rock protolith. Protolith undergoes high temperature and high-pressure processes, which also cause a physical and chemical change in the rock. Moreover, a protolith can be a sedimentary rock, igneous rock or an existing metamorphic rock. Figure 3: A Foliated Structure Moreover, we can observe a layered pattern in a cross-section of the metamorphic rock. We call this foliation. This foliation occurs when a rock is shortened on one axis during the process of recrystallization. However, there are non-foliated structures as well. The rocks that undergo uniform pressure and temperature on all the sides form non-foliated rocks. DefinitionIgneous rocks are a type of rocks that form due to the solidification of lava or magma while sedimentary rocks are a type of rocks that form via accumulation or deposition of sediment materials. In contrast, metamorphic rocks form from the transformation of an existing rock type into a new rock type. FormationIgneous rocks form from magma or lava while sedimentary rocks from sediment materials and minerals or organic matter, and metamorphic rocks form from igneous rocks, sedimentary rocks or an existing metamorphic rock. OccurrenceMoreover, igneous rocks cover about 80% of Earth’s crust while sedimentary rocks cover about 80% of Earth’s crust. In addition, metamorphic rocks cover about 12% of Earth’s surface. ConclusionThere are three basic types of rocks as sedimentary, igneous and metamorphic rocks which are classified according to the method of formation. The main difference between igneous sedimentary and metamorphic rocks is that igneous rocks form from magma or lava and sedimentary rocks form from accumulation or deposition of small particles whereas metamorphic rocks form from the transformation of an existing rock type into a new form. Reference:1. “Igneous Rocks.” National Geographic Society, 5 Sept. 2019, Available here. Image Courtesy:1. “Kanaga Volcano (22432739869)” By Michelle Combs, USGS – (Public Domain) via Commons Wikimedia Sedimentary rocks are formed on or near the Earth’s surface, in contrast to metamorphic and igneous rocks, which are formed deep within the Earth. The most important geological processes that lead to the creation of sedimentary rocks are erosion, weathering, dissolution, precipitation, and lithification. Erosion and weathering include the effects of wind and rain, which slowly break down large rocks into smaller ones. Erosion and weathering transform boulders and even mountains into sediments, such as sand or mud. Dissolution is a form of weathering—chemical weathering. With this process, water that is slightly acidic slowly wears away stone. These three processes create the raw materials for new, sedimentary rocks. Precipitation and lithification are processes that build new rocks or minerals. Precipitation is the formation of rocks and minerals from chemicals that precipitate from water. For example, as a lake dries up over many thousands of years, it leaves behind mineral deposits; this is what happened in California’s Death Valley. Finally, lithification is the process by which clay, sand, and other sediments on the bottom of the ocean or other bodies of water are slowly compacted into rocks from the weight of overlying sediments. Sedimentary rocks can be organized into two categories. The first is detrital rock, which comes from the erosion and accumulation of rock fragments, sediment, or other materials—categorized in total as detritus, or debris. The other is chemical rock, produced from the dissolution and precipitation of minerals. Detritus can be either organic or inorganic. Organic detrital rocks form when parts of plants and animals decay in the ground, leaving behind biological material that is compressed and becomes rock. Coal is a sedimentary rock formed over millions of years from compressed plants. Inorganic detrital rocks, on the other hand, are formed from broken up pieces of other rocks, not from living things. These rocks are often called clastic sedimentary rocks. One of the best-known clastic sedimentary rocks is sandstone. Sandstone is formed from layers of sandy sediment that is compacted and lithified. Chemical sedimentary rocks can be found in many places, from the ocean to deserts to caves. For instance, most limestone forms at the bottom of the ocean from the precipitation of calcium carbonate and the remains of marine animals with shells. If limestone is found on land, it can be assumed that the area used to be under water. Cave formations are also sedimentary rocks, but they are produced very differently. Stalagmites and stalactites form when water passes through bedrock and picks up calcium and carbonate ions. When the chemical-rich water makes its way into a cave, the water evaporates and leaves behind calcium carbonate on the ceiling, forming a stalactite, or on the floor of the cave, creating a stalagmite. |
What are the two main properties of sedimentary rock that distinguish them from igneous and metamorphic rock?
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