Igneous rock is one of the glossy or crystalline rocks formed by the solidification and cooling of molten magma. When the rock is heated at high temperature under the Earth’s crust, then Magma forms igneous rocks that are strong. They are one of the three types of rocks, the two others being Sedimentary and Metamorphic. The most common igneous rocks are Granite and Basalt but they have a different textures and compositions. Basalt is darker and it has a fine grained configuration of magma intrusions and lava flow. Its dark minerals are rich in Iron and Magnesium. So it is called a Mafic rock. Granite is a light and coarse grained rock and it exposed after deep erosion and formed at great depth. It is rich in Quartz and Feldspar, so it is called a Felsic Rock.
Igneous rocks are mainly formed in the three places, primarily at the point of pull apart of the tectonic plates, secondarily, Subduction Zones (where the plates come together) and finally, where the Continents push against each other. These actions make Earth’s crust thicker.
Origin of Name
The name has been derived from the Latin word “Ignis”, which means fire.
Classification of Igneous rocks is based upon minerals they contain. Main minerals of this rock are hard and they are Quartz, Amphiboles, Pyroxenes and Feldspar. These are called dark minerals. 95% of Earth’s crust is made up of igneous rock.
Types of rocks
There are two Kinds of Igneous rocks-
Extrusive Rock- It is also known as volcanic rock, and it is formed at the surface of the crust. It solidifies and cools quickly and it has microscopic and invisible grains. This rock is formed of lava. This rock is fine grained, crystalline and smooth. Common extrusive rock is Basalt, it forms lava sheets, lava plateaus and lava flows. It is produced in the Divergent boundary, Convergent boundary and hotspot.
Intrusive Rock, known also as Plutonic Rocks is formed from magma that solidifies and cools in the crust of the Earth. It is enclosed by pre-existing rock which is called country rock. This rock cools more slowly and it has visible grains of medium to small size. It has large mineral crystals that are so easy to see. Gabro is an intrusive rock and it contains rich amounts of Silver, Chromium and Gold. It is also used as a crush stone for road metal, railroad ballast and for concrete aggregate. And it is known as black granite.
Igneous rock can be used in different ways. Pumice, Granite and Basalt igneous rocks are very useful. Granite is a durable and hard igneous rock and it is made up of apparent visible crystals of many minerals. When it is polished it looks good. It is often used for expensive kitchen counters, gravestones and Worktops and also in creating frontage of buildings. It is also used as an ornamental stone, in monuments and architectural construction. It is rich in potassium, Silica, Quartz and Sodium. But it is low in Iron, Magnesium and Calcium. Basalt is a also very useful rock and is fine grained. It is a dark colored rock and It is one of the main rocks that form the oceanic crust. It is used as an ingredient of concrete and also a good source of iron. Pumice is a porous and light rock; sometimes it can float on water. It is formed in volcanic eruptions. It is formed when the gas is released violently from the silent molten rock. This process creates a rock with many tiny bubbles in it. Pumice stone is used to remove dead skin of the feet and is also used in emery boards, hand soaps and harsh cleaning products. It is also used in lightweight construction material, as an ingredient.