If you are a geography student, preparing for government exams or want to explore India, this video/post will help you in understanding classification of Indian Rocks.
The classification of Indian rocks is primarily based on their origin, formation processes, and composition. This classification divides rocks into three main types:
1. Igneous Rocks
These rocks are formed by the cooling and solidification of molten magma or lava. They are called primary rocks because they form the foundation of the Earth’s crust.
Types:
- Intrusive Igneous Rocks: Formed when magma cools slowly beneath the Earth’s surface. They have larger crystals due to slow cooling (e.g., granite, diorite).
- Extrusive Igneous Rocks: Formed when lava cools rapidly on the Earth’s surface. They have smaller or no crystals due to rapid cooling (e.g., basalt, pumice).
Examples in India:
- Deccan Traps (basaltic lava flows in Maharashtra and surrounding regions).
- Granite formations in Rajasthan.
2. Sedimentary Rocks
These rocks are formed by the accumulation and compaction of sediments over time. The sediments may be derived from pre-existing rocks, biological remains, or chemical precipitation.
Types:
- Clastic Sedimentary Rocks: Made from mechanical weathering debris (e.g., sandstone, shale).
- Chemical Sedimentary Rocks: Formed by precipitation of minerals from water (e.g., limestone, gypsum).
- Organic Sedimentary Rocks: Composed of organic material like plant remains or shells (e.g., coal, chalk).
Examples in India:
- Sandstone of the Vindhyan Range.
- Limestone in the Narmada and Chambal basins.
- Coal deposits in Jharkhand and West Bengal.
3. Metamorphic Rocks
These rocks are formed when existing rocks (igneous, sedimentary, or older metamorphic rocks) are subjected to high temperature, pressure, or chemically active fluids, causing changes in their mineral composition and texture.
Types:
- Foliated Metamorphic Rocks: Exhibit a banded or layered appearance due to pressure (e.g., gneiss, schist).
- Non-foliated Metamorphic Rocks: Do not have a layered structure (e.g., marble, quartzite).
Examples in India:
- Gneiss in the Peninsular region (e.g., Bengal Gneiss).
- Marble in Rajasthan (e.g., Makrana marble).
- Quartzite in the Aravalli Hills.
Additional Classifications Based on Indian Context
- Precambrian Rocks: Found extensively in the Peninsular Shield. Includes Dharwar and Archaean rocks rich in minerals like iron, gold, and manganese.
- Gondwana Rocks: Found in coal-bearing formations like the Damodar Valley.
- Deccan Traps: Basaltic lava flows from volcanic activity during the Cretaceous-Paleogene period.
Economic Importance:
- Igneous Rocks: Source of minerals like iron, mica, and feldspar.
- Sedimentary Rocks: Provide building materials (sandstone, limestone) and fossil fuels (coal, petroleum).
- Metamorphic Rocks: Valuable for construction and ornamental purposes (marble, slate).
This classification underpins the geological diversity and resource wealth of India.
