Rock Systems of India
Indian geologists classify rocks into five great groups, from oldest to youngest.
1. Archaean System (oldest)
- Formed when the earth's crust cooled; no fossils.
- Gneiss and schists; two types: Archaean granite and gneiss (Bundelkhand gneiss, Banded Gneissic Complex) and Dharwar.
- Found in Karnataka, Tamil Nadu, Andhra Pradesh, Odisha, Rajasthan, Jharkhand; core of the Peninsula.
- Minerals: mica, iron ore, manganese, copper, chromite, gold.
2. Dharwar System
- First sedimentary rocks turned into metamorphic ones; named after Dharwar (Karnataka).
- Rich in iron ore, manganese, gold (Kolar), copper, chromite, mica and building stones (granite). Found in Karnataka (Dharwar-Bellary), Aravalli, Jharkhand, Odisha, Maharashtra.
- Major source of mineral wealth. Hence "Dharwar = metal rocks".
3. Cuddapah System
- Named after the Cuddapah district (Andhra Pradesh). Mostly shales, quartzites, limestones of the Proterozoic.
- Found in Andhra Pradesh, Chhattisgarh, parts of Uttarakhand, with a basin shape.
- Minerals: asbestos, cement-grade limestone, marble, slate, copper, cobalt, diamond in Kurnool.
4. Vindhyan System
- Sedimentary rocks in a vast basin between Sasaram (Bihar) and Chittorgarh (Rajasthan), with sandstone, limestone and shale; no igneous activity; no fossils to speak of.
- Best building stones: red sandstone used for the Red Fort, Fatehpur Sikri, Sanchi Stupa, and diamonds at Panna (Madhya Pradesh) and Golconda.
- Also cement-grade limestone, glass sand.
5. Palaeozoic (Cambrian to Carboniferous)
- Marine fossil-bearing rocks of the Kashmir, Spiti, Kumaon, Himachal region; Haimanta, Spiti and Kashmir sequences; also in Salt Range (Pakistan).
- Minerals: little economic value; fossils of trilobites.
6. Gondwana System
- Late Carboniferous to Jurassic, about 300-150 Ma; terrestrial rocks with plant fossils; found in river valleys formed by faults: Damodar, Mahanadi, Godavari, Son, Narmada.
- 98 per cent of India's coal is in the Gondwana beds (the rest is Tertiary coal in Assam, Rajasthan, J&K, Tamil Nadu).
- Also iron ore, limestone, sandstone; plant fossil Glossopteris proves the Gondwana connection.
7. Deccan Trap
- Cretaceous-Eocene basalt lava; covers about 5 lakh sq km of Maharashtra, Gujarat, Madhya Pradesh, Karnataka, Telangana, Andhra Pradesh.
- Weathers into black cotton soil (regur); minerals scarce, but bauxite at laterite caps; zeolite and agate.
8. Tertiary System
- Eocene to Pliocene (66-2 Ma). The Himalayas and Shiwaliks belong here.
- Oil and natural gas (Assam, Gujarat, Bombay High). Coal and lignite: Neyveli, Cambay.
9. Quaternary System
- Pleistocene and Holocene; the alluvial plains, Bhangar and Khadar, Karewas, desert sands, delta deposits.
- Great alluvial plains formed here; no mineral but the most fertile.
Summary table
| System | Age | Rock type | Key resource |
|---|---|---|---|
| Archaean | Oldest | Gneiss, schist | Mica, gold, iron |
| Dharwar | Pre-Cambrian | Metamorphic | Iron, manganese, gold, copper |
| Cuddapah | Proterozoic | Shale, quartzite | Asbestos, limestone |
| Vindhyan | Proterozoic | Sandstone, limestone | Building stone, diamond |
| Palaeozoic | 540-250 Ma | Marine | Fossils |
| Gondwana | 300-150 Ma | Terrestrial | Coal (98%) |
| Deccan Trap | ~66 Ma | Basalt | Black soil |
| Tertiary | 66-2 Ma | Folded sediments | Oil, gas, lignite |
| Quaternary | 2 Ma to now | Alluvium | Soil |
Keep practising
Notes are only half the work. Test yourself with questions and discuss doubts with other aspirants.
Prepared for exam revision from NCERT, standard geography textbooks, the Census of India 2011, the India State of Forest Report, IMD, Ministry of Agriculture and other official sources. Maps are schematic teaching maps, not Survey of India maps, and zone boundaries are approximate. Figures such as production, capacity, counts of parks and ports, and census status change, so check the latest official source before relying on them. Found a mistake? Tell us.