The Differences Between Sedimentary Rocks and Igneous Rocks

Differences Between Sedimentary Rocks and Igneous Rocks 

Igneous and sedimentary rocks are the two main types of rocks found on Earth. They are formed in different ways and have different properties.

1-Sedimentary and Igneous Rocks 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.

Differences Between Sedimentary Rocks and Igneous Rocks
The Difference Between Sedimentary Rocks and Igneous Rocks

2-Distribution: Abundance on the Earth Crust

Sedimentary rocks are the most common type of rock on Earth's surface. They cover about 75% of the Earth's land area. 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-Sedimentary and Igneous Rocks Mineral Composition

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.

Igneous rocks are composed of minerals that have crystallized from magma or lava. The composition of an igneous rock depends on the chemical composition of the magma or lava. 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.


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.

5-Sedimentary and Igneous Rocks Structures

Sedimentary rocks can have a variety of structures, such as bedding, ripple marks, and cross-bedding. 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.

Igneous rocks can also exhibit a variety of structures, such as vesicles, amygdules, and columnar jointing. These structures are formed by the processes of cooling and solidification. 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-Sedimentary and Igneous Rocks Classification

Based on the processes responsible for their formation, sedimentary rocks can be subdivided into four groups: clastic sedimentary rocks, biochemical (or biogenic) sedimentary rocks, chemical sedimentary rocks and a fourth category for "other" sedimentary rocks formed by impacts, volcanism, and other minor processes.

Igneous rocks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body.

7-Sedimentary and Igneous Rocks Importance & Uses

Sedimentary rocks are used in a variety of ways, including construction materials, abrasives, and chemicals. Sedimentary rocks are also used to produce fossil fuels, such as coal and oil. Coal and oil shale are found in sedimentary rocks. A large proportion of the world's uranium energy resources are hosted within sedimentary successions.sedimentary rocks contain a large proportion of the Earth's groundwater aquifers. Our understanding of the extent of these aquifers and how much water can be withdrawn from them depends critically on our knowledge of the rocks that hold them (the reservoir).

Many types of igneous rocks are used as building stone, facing stone, and decorative material, such as that used for tabletops, cutting boards, and carved figures. Pumice is used as an abrasive material in hand soaps, emery boards, etc.

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