Three Types Of Rock Essay

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The three types of rocks that comprise the rock cycle are igneous, sedimentary, and metamorphic rock. Rocks are grouped into one of these three categories based upon how they are formed (Thompson & Turk, 2007). Igneous rock is formed from magma and depending if it solidifies quickly or slowly on the Earth’s surface or in the Earth’s crust will determine the texture and if it crystallizes. For instance, magma that cools rapidly does not have time to form crystals and it creates a type of volcanic glass called obsidian. Magma that solidifies in Earth’s crust will cool slowly, form crystals over a long period of time, and form a rock such as granite. Igneous rocks that are formed on Earth’s surface are called extrusive rocks and igneous rocks …show more content…
Extrusive igneous rocks are fine grain and intrusive igneous rocks are coarse grain. Igneous rocks are categorized into felsic, intermediate, mafic, and ultramafic depending on the volume of the minerals and the mineral content in the rock. For instance, granite is considered a coarse grain felsic rock and basalt is considered a fine grain mafic rock. Sedimentary rock is formed by a process called lithification and it is made up of weathered rocks and dead marine organisms such as clay, sand, gravel, shells, and corals. Sedimentary rocks are categorized into four different groups such as clastic, organic, chemical, and bioclastic. Clastic sedimentary rock is composed of gravel, sand, silt, or clay and is formed by the accumulation of sediment. Once the sediment has accumulated it becomes compacted and the lithification process cements the sediment together creating a clastic sedimentary rock. Clastic rocks such as sandstone, siltstone, and shale make up more than 85% of all sedimentary rocks (Thompson & Turk, 2007). Organic sedimentary rock is composed of the remains of plants and animals and is formed from the compaction of overlying

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