Types of Igneous Rocks and their Occurrences

Igneous rocks are formed through the solidification of magma or lava. They are classified based on their mineral composition, texture, and mode of occurrence. In the syllabus of the UPSC exam, there are several specific types of igneous rocks and their occurrences mentioned. Let's explore them in detail below:

1. Granite:
- Granite is a coarse-grained igneous rock composed mainly of quartz, feldspar, and mica.
- It is widely distributed and occurs in various parts of the world.
- In India, granite is found in the states of Tamil Nadu, Karnataka, Andhra Pradesh, Rajasthan, and Odisha.
- It is used extensively as a building material and for ornamental purposes.

2. Basalt:
- Basalt is a fine-grained igneous rock that is dark in color due to its high iron and magnesium content.
- It is one of the most common types of igneous rocks and is found all over the world.
- In India, basalt occurs in the Deccan Traps of Maharashtra, Madhya Pradesh, Gujarat, and Rajasthan.
- Basalt is used for construction, road aggregates, and as a raw material for the production of crushed stone.

3. Dolerite:
- Dolerite is a medium-grained igneous rock that is similar to basalt but contains more plagioclase feldspar.
- It is commonly found in dikes, sills, and other intrusive formations.
- In India, dolerite occurs in the Deccan Traps and in the Eastern Ghats.
- Dolerite is used as a crushed stone for road construction and as a source of building material.

4. Rhyolite:
- Rhyolite is a fine-grained igneous rock that is similar to granite but has a higher silica content.
- It is commonly associated with volcanic activity.
- Rhyolite occurs in the Western Ghats and the Satpura Range in India.
- It is used as a decorative stone and for the production of crushed stone.

5. Andesite:
- Andesite is an intermediate igneous rock that is fine-grained and typically gray in color.
- It is commonly found in volcanic arcs and subduction zones.
- In India, andesite occurs in the Himalayas, particularly in the states of Himachal Pradesh and Uttarakhand.
- Andesite is used as a construction material and for decorative purposes.

6. Pegmatite:
- Pegmatite is a coarse-grained igneous rock that is characterized by exceptionally large crystals.
- It is often associated with the final stages of crystallization in a magma chamber.
- Pegmatite occurrences in India include the states of Rajasthan, Jharkhand, and Maharashtra.
- Pegmatite is valued for its gemstones, rare minerals, and as a source of industrial minerals.

Overall, the syllabus of the UPSC exam includes the study of specific types of igneous rocks and their occurrences. Understanding these rocks and their geological significance is crucial for candidates preparing for the exam.