Igneous Rocks

Rocks are the fundamental units of Earth, creating everything on its crust, from towering mountains to the flat ground beneath our feet. These rocks are formed in different ways, which gives them different properties and morphology. One such rock is igneous rock, which comes into being when molten lava cools and hardens. Igneous rocks are used in various industries and for daily purposes, making it even more important to examine the composition of these rocks. Here, we will get into the basics of these rocks, from their formation to their uses in different industries. 

1.0Understanding Igneous Rocks

Igneous rocks are one of the three large groups of Earth's rocks, the other two being sedimentary and metamorphic rocks. They are created by the solidification of molten rock, either magma under the surface of the Earth or lava that is erupted above the Earth's surface. The term "igneous" is derived from the Latin term "ignis," meaning fire, which ultimately gives information about its origin. Some major examples of igneous rocks are granite, basalt, gabbro, and many more. 

2.0Types of Igneous Rocks

Igneous rocks are mainly divided into two different types of igneous rocks based on the location of their formation: 

1. Intrusive Igneous Rocks: These types of rocks are formed inside the Earth by the slow cooling of the magma. The slow cooling gives these rocks a crystalline igneous rock texture. These rocks are characterised by their large, crystal-grained texture visible to the naked eye. Igneous rocks are generally formed in the region of collision between tectonic plates, such as mountain ranges. Examples of intrusive igneous rocks include granite, diorite, and gabbro. 

2. Extrusive Igneous Rocks: These rocks are generally formed after a volcanic eruption, when lava cools rapidly on the surface of Earth. This fast cooling also results in small crystals or a glassy texture finish in some cases. The crystals of these rocks are too small, so that they can not even be seen with the naked eye, ultimately forming a glassy rock-like structure. Examples of extrusive igneous rocks include basalt, pumice, obsidian, and andesite.

3.0Formation of Igneous Rocks

Igneous rocks are created when molten rock material, also known as magma, cools and solidifies. The rate of cooling of magma or lava determines the mineral content and the texture of the igneous rocks. Note that: 

• Magma is molten rock below the Earth's crust.
• Lava is magma that has risen to the surface due to volcanic eruptions.

Igneous rock formation is one of the most important processes in the rock cycle, and the rate of cooling of the molten material decides whether the rock falls under the category of intrusive igneous rocks or extrusive igneous rocks.

4.0Properties of Igneous Rocks

There is a wide range of characteristics of igneous rocks that set them apart from other types of rocks, which include: 

1. Texture: The texture is the detail of rock in terms of its constituent parts, like size, shape, and arrangement of particles. The texture can be of a different type for each rock, indicating the rate of cooling of the material. For instance: 

• Coarse-grained (e.g., granite): Slow cooling; big crystals.
• Fine-grained (e.g., basalt): Fast cooling; little crystals.
• Glassy (e.g., obsidian): Very fast cooling; no crystals.
• Porphyritic: Combination texture with big and little crystals.
• Vesicular or Frothy (e.g., pumice): Has bubbles from gas.

2. Hardness: Almost every igneous rock is very hard and durable, making them an ideal choice for construction projects such as granite countertops, road stones, etc. 
3. Colour: The Colour of igneous rocks generally depends on their mineral composition, for example: 

• Felsic rocks (rich in silica): Light-colored (e.g., granite, rhyolite).
• Mafic rocks (rich in iron and magnesium): Dark-colored (e.g., basalt, gabbro).
• Intermediate rocks: Contain a combination of light and dark minerals. 
• Ultramafic: Very low in silica, rich in iron and magnesium, hence possesses a dark colour. 

4. Density: The density of each type of igneous rock can also vary based on the type of mineral present in it. For example, mafic rocks are denser than felsic ones due to the presence of heavy minerals; similarly, granite is less dense than basalt, a type of rock. 
5. Crystalline Structure: All igneous rocks, except some, show a crystalline structure, meaning their minerals are formed in an interlocking crystal structure.  
6. Resistance to Weathering and Erosion: Generally, igneous rocks do not get affected by weathering and erosion. Therefore, these rocks form long-lasting structures in natural as well as human-made landscapes. 
7. Jointing and Fracturing: During cooling, igneous rocks often form joints or fractures in them, ultimately influencing how rocks break and making the water move through them. 

5.0Uses of Igneous Rocks

Due to their long-lasting strength, stability, and amazing appearance, igneous rocks are used in a number of fields, including: 

1. Construction and Building Materials: Granite, a famous example of igneous rocks, is widely used in the construction of monuments, floor tiles, and countertops. Another example of construction type igneous rocks is basalt, which is mainly used to build roads, railway ballast, etc. 
2. Decorative and Architectural Uses: Igneous rocks are also used for constructing decorative objects and jewellery. For example, obsidian, a volcanic glass, is specifically used for this purpose due to its glossy black appearance.  
3. Industrial Applications: Some rocks of igneous types, such as pumice, are also used as an abrasive in polishing, cleaning, and exfoliating products. 
4. Filter and Drainage Systems: Pumice is also used in water filtration systems and drainage layers, due to its lightweight and porous structure. 
5. Soil Improvement in Agriculture: Finely grained igneous rocks like basalt rock dust are largely used as soil conditioners due to their mineral retention properties to enhance soil health.