The Differences Between Sedimentary 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: Formed from the cooling and solidification of magma (molten rock) or lava (molten rock that erupts onto the surface). Magma cools and solidifies either underground (intrusive) to form plutonic rocks like granite, or above ground (extrusive) to form volcanic rocks like basalt.

Sedimentary Rocks: Formed through the accumulation and compaction of sediments (fragments of pre-existing rocks, minerals, and organic matter) over time. These sediments can be transported by wind, water, or glaciers before being deposited and lithified (transformed into solid rock) through processes like cementation (minerals filling pore spaces) or compaction (pressure squeezing out water and air).

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.

Igneous Rocks: Igneous rocks are less abundant on the Earth's surface compared to sedimentary rocks but can still be found in various locations. They are often associated with volcanic activity, mid-ocean ridges, and areas of tectonic activity.

3- Mineral Composition

Sedimentary Rocks: Sedimentary rocks are primarily composed of mineral grains derived from the weathering and erosion of pre-existing rocks. Common minerals found in sedimentary rocks include quartz, feldspar, calcite, clay minerals, and gypsum.

Igneous Rocks: Igneous rocks form from the solidification of molten rock material (magma or lava). They are composed of interlocking mineral crystals that crystallize from the cooling of magma or lava. Common minerals found in igneous rocks include quartz, feldspar, mica, amphibole, and olivine.


Sedimentary Rocks: Often contain fossils of plants and animals that were buried in the sediments over time. These fossils provide valuable information about past life forms and environmental conditions. Fossils can be preserved in sedimentary rocks due to the processes of sedimentation and lithification (the process of sediment transforming into rock).

Igneous Rocks: Almost never contain fossils because the high temperatures associated with molten magma would destroy any organic material present.

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-Geological Setting

Sedimentary Rocks: Sedimentary rocks form in a wide range of geological settings, including river valleys, lake beds, coastal areas, and continental shelves. They are associated with processes such as weathering, erosion, transportation, deposition, compaction, and cementation.

Igneous Rocks: Igneous rocks form in various geological settings, including volcanic areas, mid-ocean ridges, and areas of tectonic activity where magma intrudes into the Earth's crust. They are associated with processes such as melting, magma ascent, and cooling.


Sedimentary Rocks: Generally weaker and less hard compared to igneous rocks because they are formed from the compaction and cementation of often loose sediments. However, their hardness can vary depending on the mineral composition and the degree of cementation.

Igneous Rocks: Generally harder and more durable due to the crystallization of minerals from molten rock. Their hardness can also vary depending on the mineral composition and the rate of cooling and crystallization.

9-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.

Understanding these key differences will help you differentiate between sedimentary and igneous rocks and gain a deeper understanding of the geological processes that shape our planet.

Read also: Top 7 Differences between Metamorphic rocks and Igneous rocks
The Differences Between Sedimentary and Metamorphic Rocks

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