Igneous rock: Formation, types, characteristics, and examples

What are igneous rocks?

Igneous rock is one type of rock. The cooling and crystallization of magma form the igneous rock. Igneous rocks were the first formed rocks on Earth. So, igneous rock often referred to as primary rocks. Most of the earth’s crust consists of igneous rocks.

igneous rock

How igneous rock is formed?

 

 our earth’s crust is a solid part of the earth. below the earth’s crust, there is a hot molted semi-liquid exist called a magma. the magma collects in the magma chamber that exists below the earth’s crust.

when magma rises and reaches to earth’s surface is called lava. However, most of the risen magma remains trapped beneath the Earth’s surface. Igneous rock formed by cooling, crystallization, and solidification of magma and lava.

      what is the crystallization of magma?

           As we know magma is semi-liquid molten minerals or rocks. when the magma starting to cool, the grain of individual minerals grows in a cooling magma. a grain is the distinct oriented crystals.  the rate of cooling determines the growth of grains. if magma cools rapidly then grains size is small. and if magma cools slowly then grain size is bigger.

 

Types of igneous rocks

Depending on the rate of magma cooling, there are two types of igneous rocks: 

  • extrusive igneous rocks or volcanic igneous rocks and
  • intrusive igneous rock.

Extrusive igneous rocks

 extrusive igneous rock is often called volcanic igneous rock. when magma reaches on the surface of the earth is called lava. on the surface of the earth, the lava cools rapidly and the grains don’t have sufficient time to become large. Thus, the igneous rock formed by rapid cooling and solidification of lava is called a volcanic igneous rock.

 the basalt rock one of the examples of volcanic igneous rock.

Intrusive igneous rock

 Plutonic igneous rocks form below the surface of the earth. when magma rises in the crust, it mostly remains trapped in the crust. here, the magma cools slowly. as a result, mineral grains have sufficient time to become larger. Thus, the intrusive igneous rock is formed by slow cooling and solidification of magma.

When the magma cools and solidifies deep in the crust, it is called a plutonic igneous rock. granite is the example of plutonic igneous rocks.

another type of intrusive igneous rock is hypabyssal rock. hypabyssal rock is formed in the shallow crust. it has an intermediate size of grains. dolerite is an example of a hypabyssal rock.

Characteristics of igneous rocks

  • Igneous rocks don’t contain any fossils
  • there is no layer found in igneous rock
  • Igneous rocks are hard and do not contain holes
  • igneous rocks are rich in minerals

Examples of igneous rocks

1. basalt

    igneous rock, examples of igneous rock

basalt is the most common rock on earth. the oceanic crust mostly made up of basalt. basalt consists of feldspar, pyroxene, and olivine. the pyroxene and olivine present in basalt give it dark grey or dark green color.

 

2. Rhyolite

   If magma consists larger amount of sodium, silica, and potassium with a lesser amount of iron and magnesium form the rhyolites rock. rhyolite consists of quartz and potassium feldspar. It looks yellow, white, grey, or red.

3. Granite

igneous rock

 

 

 

granite is mostly found in the continental crust. granite is a light-colored and silica-reach rock. Granite consists of feldspar and quartz minerals.Granites are found in granular and phaneritic texture. Granites are the natural source of radiation.

4. Gabbro

Gabbro is a dark and coarse-grained intrusive igneous rock. Gabbro composed of mainly calcium feldspar and pyroxene with a lesser amount of olivine and hornblende.

5.Diorite

diorite is a speckled black and white intrusive igneous rock. it primarily composed of sodium feldspar, calcium feldspar, and hornblend. it consists of minor amounts of pyroxene and biotite.

6. Andesite

         Andesite is grey and fine-grained rock. it has a similar kind of composite to diorite.

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