Explain the differences between the Igneous Rocks and the Sedimentary Rocks.
Answers
Answer:
1-Formation
Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.
Sedimentary Rocks formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle and accumulate or minerals to precipitate from a solution.
2-Abundance on the earth crust
The sedimentary rock cover of the continents of the Earth's crust is extensive, but the total contribution of sedimentary rocks is estimated to be only 8% of the total volume of the crust.
Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earth's crust by volume.
3-Mineralogical contents
Felsic Igneous rock, highest content of silicon, with predominance of quartz, alkali feldspar and/or feldspathoids: the felsic minerals; these rocks (e.g., granite, rhyolite) are usually light coloured, and have low density. While mafic Igneous rock, lesser content of silicon relative to felsic rocks, with predominance of mafic minerals pyroxenes, olivines and calcic plagioclase; these rocks (example, basalt, gabbro) are usually dark coloured, and have a higher density than felsic rocks.ultramafic rock, lowest content of silicon, with more than 90% of mafic minerals.
Most sedimentary rocks contain either quartz (especially siliciclastic rocks) or calcite (especially carbonate rocks). In contrast with igneous and metamorphic rocks, a sedimentary rocks usually contains very few different major minerals. However, the origin of the minerals in a sedimentary rock is often more complex than those in an igneous rock. Minerals in a sedimentary rock can have formed by precipitation during sedimentation or diagenesis. In the second case, the mineral precipitate can have grown over an older generation of cement.
4-fossils
Among the three major types of rock, fossils are most commonly found in sedimentary rock. Unlike most igneous and metamorphic rocks, sedimentary rocks form at temperatures and pressures that do not destroy fossil remnants. Often these fossils may only be visible when studied under a microscope (microfossils) or with a loupe.
5-Structures
Structures in sedimentary rocks can be divided into 'primary' structures (formed during deposition) and 'secondary' structures (formed after deposition). Structures are always large-scale features that can easily be studied in the field.
The structures of igneous rocks are large scale features, which are dependent on several factors like: (a) Composition of magma.(b) Viscosity of magma. (c) Temperature and pressure at which cooling and consolidation takes place. (d) Presence of gases and other volatiles.
6-Classification
Igneous rohe processes responsible for their formation, s
cks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body.
Based on t
Igneous rocks are formed from the cooling and solidification or crystallisation of magma or lava, whereas, sedimentary rocks are formed from the compaction and cementation of sediments.
Explanation:
Differences between the Igneous Rocks and the Sedimentary Rocks are as follows:
1. Igneous rocks are hard and compact.
Sedimentary rocks are softer than igneous rocks and easily eroded.
2. All igneous rocks are crystalline in nature.
Sedimentary rocks are formed due to aggregation and compaction of sediments, chiefly river sediments.
3. Igneous rocks do not have layers and do not contain fossils because they are formed by the cooling and solidification of molten rock materials in which life forms do not survive.
Sedimentary rocks have a horizontal layered arrangement, one above the other. Hence, they are known as stratified rocks. They contain fossils of animals and plants.
4. Igneous rocks are termed as primary rocks because other types of rocks are formed directly or indirectly from igneous rocks.
Sedimentary rocks being of secondary origin; they are also called secondary rocks.
5. Some examples of igneous rocks are basalt, obsidian, andesite, rhyolite, Granite, and dolerite.
Some examples of sedimentary rocks are sandstone, shale, limestone, gypsum, and conglomerate.
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