Rocks and Minerals
~10 min read
- Three rock types: Igneous (from cooled magma/lava), Sedimentary (compacted sediments), Metamorphic (transformed by heat/pressure).
- Rock cycle: All three types convert into each other over geologic time.
- Indian distribution: Gondwana coal in Damodar valley; iron ore in Singhbhum/Bailadila; bauxite in Odisha/Jharkhand; mica in Rajasthan; gold in Karnataka (Kolar).
Rocks are aggregates of minerals; minerals are pure chemical compounds with a defined composition. The three rock types — igneous, sedimentary, metamorphic — are linked by the rock cycle. NDA asks about specific examples and India's mineral distribution.
Igneous Rocks
Formed by cooling and solidification of magma (below surface = intrusive/plutonic) or lava (above surface = extrusive/volcanic).
| Rock | Type | Note |
|---|---|---|
| Granite | Intrusive | Coarse-grained; light colour; building stone |
| Basalt | Extrusive | Fine-grained; dark; Deccan Plateau is mostly basalt |
| Pumice | Extrusive | Light, frothy, floats on water |
| Obsidian | Extrusive | Volcanic glass, no crystals (rapid cooling) |
Sedimentary Rocks
Formed by compaction and cementation of sediments. Often layered (stratified). Contain most of the world's fossils.
- Clastic (mechanical): sandstone, shale, conglomerate
- Chemical: rock salt, gypsum, some limestones
- Organic: coal (plant remains), most limestones (shell debris)
India: Vindhyan sandstones (used in Red Fort and Qutub Minar); Gondwana coal beds (Damodar valley).
Metamorphic Rocks
Formed when existing rocks are subjected to heat, pressure, or chemically active fluids — but stay solid (no melting).
| Parent rock | Metamorphic equivalent |
|---|---|
| Limestone | Marble |
| Sandstone | Quartzite |
| Shale/Clay | Slate → Phyllite → Schist → Gneiss (increasing metamorphism) |
| Granite | Gneiss |
| Coal | Anthracite → Graphite → Diamond (extreme) |
Mineral Distribution in India
| Mineral | Where found |
|---|---|
| Iron ore | Singhbhum (Jharkhand), Bailadila (Chhattisgarh), Bellary (Karnataka), Goa |
| Coal | Damodar valley (Jharia, Raniganj, Bokaro), Singrauli, Talcher |
| Bauxite | Odisha (largest), Jharkhand, Gujarat |
| Manganese | Odisha, Karnataka, Maharashtra |
| Mica | Jharkhand, Rajasthan, Andhra Pradesh |
| Copper | Khetri (Rajasthan), Singhbhum, Madhya Pradesh |
| Gold | Kolar and Hutti (Karnataka) |
| Uranium | Jaduguda (Jharkhand) |
| Diamond | Panna (Madhya Pradesh) |
NDA PYQ Examples
Q: The Deccan Plateau is mainly composed of:
(a) Granite (b) Basalt (c) Sandstone (d) Limestone
Answer: (b) Basalt — formed from extensive lava flows ~65 million years ago.
Q: Marble is a metamorphic rock derived from:
(a) Sandstone (b) Limestone (c) Granite (d) Shale
Answer: (b) Limestone.
Q: India's largest bauxite-producing state is:
(a) Jharkhand (b) Odisha (c) Gujarat (d) Madhya Pradesh
Answer: (b) Odisha.
Drill Rocks and Minerals for NDA
NDA-pattern items on Rocks and Minerals with answer keys and explanations.
Start Free Mock TestFrequently Asked Questions
What is the rock cycle?
All three rock types can transform into one another over geological time. Igneous rocks weather into sediments (→ sedimentary); sedimentary rocks under heat/pressure become metamorphic; metamorphic rocks can melt and recrystallise into igneous.
Which is the oldest rock type?
Igneous — Earth's crust originally formed from cooled magma. Sedimentary and metamorphic rocks all derive ultimately from igneous originals.
Why is the Deccan Plateau black?
The Deccan Trap consists of basalt — a dark, iron-rich volcanic rock. Weathering of basalt produces the fertile black cotton soil (regur) of central India.
What is the difference between rock and mineral?
A mineral is a single chemical compound with a definite composition (e.g., quartz = SiO₂). A rock is an aggregate of one or more minerals (granite = quartz + feldspar + mica).
Where is Kohinoor diamond from?
Originally mined at Kollur in the Golconda region (Andhra Pradesh) several centuries ago. India was the world's only diamond source until Brazilian and African finds in the 18th–19th centuries.