Rocks as the base of resources, soils and landforms

Detail

1. Why rocks matter: the big link

• Rock is the base layer of the land. Three things depend on it:
• Minerals: which ores, fuels and stones are found in a place.
• Soils: what kind of soil forms when the rock breaks down (weathering).

• Landforms: what shapes the land takes. Hard rock stands up and soft rock wears down.

• Minerals are spread unevenly. Each kind of mineral forms only in rocks of a certain type and age. This is why India's mineral belts follow its rock systems.

2. Indian rock systems: a quick guide

Rock system (age)	Rock type	Main areas	What it gives
Archaean (oldest; more than about 2,500 million years old)	Granite, gneiss (crystalline: made of interlocking crystals)	Peninsular shield: Karnataka, Tamil Nadu, Chota Nagpur, Odisha	Base of the shield, red soils, granite domes, building granite, mica
Dharwar (formed just after the Archaean)	The first sedimentary rocks, later metamorphosed (changed by heat and pressure); schists	Dharwar–Bellary (Karnataka), Aravalli, Chota Nagpur, Odisha	Metallic ores such as iron, manganese, copper and gold
Cuddapah (Proterozoic)	Shale, slate, quartzite, limestone in a basin (a low, bowl-shaped area)	Cuddapah basin, Andhra Pradesh	Barytes, asbestos, uranium; quartzite ridges
Vindhyan (Proterozoic)	Sandstone, shale, limestone	From Sasaram (Bihar) to Chittorgarh (Rajasthan); Son valley	Red sandstone for buildings, limestone for cement; Panna diamonds (Madhya Pradesh)
Gondwana (roughly 300–150 million years ago)	Sandstone, shale and coal seams in trough (rift) valleys	Damodar, Son, Mahanadi, Godavari and Wardha valleys	Coal. Almost all of India's coal comes from Gondwana rocks
Deccan Traps (end of the Cretaceous period, about 66 million years ago)	Basalt (dark volcanic rock from fissure eruptions: lava pouring out of long cracks)	Maharashtra, Malwa (Madhya Pradesh), Gujarat	Black soil, step-like plateaus, rock-cut caves
Tertiary (about 66 to 2.6 million years ago)	Young sedimentary rocks	Assam, Meghalaya, Gujarat, offshore Mumbai High, Neyveli (Tamil Nadu)	Oil, natural gas, lignite, Tertiary coal
Quaternary (last 2.6 million years)	Alluvium (loose silt, sand and clay laid down by rivers)	Indo-Gangetic–Brahmaputra plains, deltas	Fertile alluvial soil but almost no minerals

3. Rock → mineral

Archaean–Dharwar shield: the store of metallic ores

• A shield is a large, very old and stable block of crystalline rock that has not been folded into mountains for a very long time. The Peninsular Plateau is India's shield.
• Chota Nagpur Plateau (Jharkhand, plus parts of Odisha, West Bengal and Chhattisgarh) is called the "storehouse of minerals" (NCERT Class 10, "Dig a little deeper").

• Iron ore (Noamundi, Singhbhum), copper (Singhbhum), mica (Koderma), bauxite and coal (in Gondwana troughs inside the plateau).

• Karnataka: iron ore at Bababudan Hills and Kudremukh, and gold at Kolar and Hutti. All are in Dharwar schists.

• Odisha: iron ore (Keonjhar, Sundargarh, Mayurbhanj), manganese and chromite (Sukinda), and bauxite on the Eastern Ghats (Koraput, Panchpatmali).
• Why metals are found here:
• Very old rocks went through many rounds of heat, pressure and magma intrusion (molten rock forcing its way into other rock).
• Hot fluids carried metals and left them in cracks as veins and lodes (thin and thick bands of ore).
• Later, long weathering (the breaking down of rock in place) washed away the useless minerals. The ore that stayed behind became richer. This is called residual or secondary enrichment. Bauxite and some iron ores are richer near the surface for this reason (NCERT Class 11, weathering and enrichment of ores).

Gondwana rocks: coal

• Cause: about 300 million years ago, thick forests grew in swampy trough valleys on the old Gondwana landmass.
• Process: the troughs slowly sank. Plant matter was buried under sand and mud. Heat and pressure over millions of years turned it into coal.
• Result: coal seams in the Damodar valley (Jharia, Raniganj, Bokaro), the Son, Mahanadi (Talcher), Godavari (Singareni) and Wardha valleys.

Tertiary rocks: oil, gas and lignite

• Oil and gas collect in young sedimentary rocks. They gather in anticlines (upward folds in rock layers) and fault traps (places where a break in the rock seals the oil in), under a cap of non-porous rock.

• Examples: Digboi and Naharkatiya (Assam), Ankleshwar (Gujarat), Mumbai High (offshore, Arabian Sea).

• Lignite is a low-grade brown coal with high moisture. Example: Neyveli, Tamil Nadu.

• Tertiary coal is younger coal found in Assam, Meghalaya, Arunachal Pradesh and Nagaland.

Quaternary alluvium: almost barren

• River deposits are young and loose. They have not had the heat, pressure or time needed to form ores. So the Ganga plain is rich in soil but poor in minerals.

4. Critical minerals: recent hooks

• Critical minerals are minerals that a country needs for its economy and security, but whose supply could easily be disrupted. Examples are lithium for electric-vehicle batteries and rare earths for magnets.
• Lithium in Reasi, J&K: in February 2023, GSI (Geological Survey of India) reported inferred lithium resources in Reasi district, Jammu and Kashmir.

• An inferred resource is the lowest level of confidence. It is an estimate from limited sampling and is not yet a proven, mineable reserve.

• Ministry of Mines list, 2023: a committee formed in November 2022 identified 30 critical minerals. The list was released in 2023 [2][3].

• The 30 are antimony, beryllium, bismuth, cobalt, copper, gallium, germanium, graphite, hafnium, indium, lithium, molybdenum, niobium, nickel, PGE (platinum group elements), phosphorus, potash, REE (rare earth elements), rhenium, silicon, strontium, tantalum, tellurium, tin, titanium, tungsten, vanadium, zirconium, selenium and cadmium [2].

• 24 of these were added to Part D of the First Schedule of the MMDR Act, 1957 (Mines and Minerals (Development and Regulation) Act). This gives the Central Government the sole power to auction their mining leases and composite licences [3].

• National Critical Mineral Mission (NCMM): launched in January 2025 for 7 years, from 2024-25 to 2030-31 [2].

• Outlay: ₹16,300 crore, plus an expected ₹18,000 crore from PSUs (public sector undertakings) and other stakeholders [2].
• GSI has been given 1,200 exploration projects to carry out between 2024-25 and 2030-31 [3].

• A Centre of Excellence on Critical Minerals (CECM) was recommended. It would update the list from time to time [3].

• Link to rocks: many critical minerals sit in old shield rocks and in pegmatites (very coarse-grained granite veins), for example lithium, beryllium, tantalum and niobium. Others form in weathered or leached zones, such as REE in laterite and bauxite. So the search follows the rock map.

5. Rock → soil

• Parent rock is the rock from which a soil forms. It decides the soil's colour, texture and minerals. Climate decides how fast the rock weathers and how much leaching happens. Leaching means rainwater washing soluble minerals down and out of the soil.

Parent rock	Process	Soil	Where in India
Basalt (Deccan Traps)	Rock weathers in place into fine clay	Black soil (regur): holds moisture, cracks deeply when dry, rich in lime, iron, magnesia and potash, poor in nitrogen and phosphorus	Maharashtra, Malwa, Gujarat (Saurashtra), and the Godavari and Krishna valleys. Best for cotton
Old granite and gneiss (Archaean)	Weathers under low to medium rain	Red soil: red from iron oxide (ferric oxide) spread through the soil; looks yellow when hydrated (wet)	Tamil Nadu, Karnataka, Odisha, Chhattisgarh, Chota Nagpur
Many rocks in hot, wet tropics	Heavy rain leaches away silica and lime. Iron and aluminium oxides are left behind	Laterite (from Latin later, brick) and bauxite (aluminium ore)	Kerala, Karnataka, Goa, Odisha hills, Meghalaya, Amarkantak–Maikal (Madhya Pradesh–Chhattisgarh)
River deposits (Quaternary)	Rivers carry silt and drop it on plains and deltas	Alluvial soil: old alluvium is bhangar (higher ground, with kankar lumps) and new alluvium is khadar (floodplain, renewed every year)	Indo-Gangetic–Brahmaputra plains; Mahanadi, Godavari, Krishna and Kaveri deltas

• Laterite as a resource: laterite becomes hard when it is cut and dried, so it is used as building brick in Kerala and Goa. The same leaching process makes bauxite ore.
• Angadipuram (Malappuram, Kerala) is a GSI National Geological Monument for laterite. Laterite was first described and named in this region of South India.

6. Rock → landform

• Main rule: differential erosion. Hard rock resists wearing away and stands high. Soft rock wears away fast and becomes low ground.

Rock	Landform	Process	Example
Granite (hard, crystalline, with joints: natural cracks)	Domes, tors and boulder hills (a tor is a pile of rounded rocks on a hilltop)	Water enters the joints → the edges weather and round off → loose material is washed away → rounded boulders are left	Hampi (on the Tungabhadra, Karnataka), Bengaluru–Mysuru region, Ramanagara
Basalt (lava laid down in flat, layered flows)	Step-like (trap) plateaus and mesas (a mesa is a flat-topped hill with steep sides; trap comes from the Swedish word for stairs)	Lava flows of different hardness lie one on top of another → the softer layers wear back → steps form	Western Ghats near Mahabaleshwar and Lonavala, Malwa Plateau
Limestone (dissolves in water)	Karst topography: land shaped by rock dissolving, with caves, sinkholes, stalactites and stalagmites	Rainwater takes in CO₂ → becomes weak carbonic acid → dissolves limestone along cracks → caves form	Borra Caves (Ananthagiri Hills, near Araku valley, Andhra Pradesh); Belum Caves (Andhra Pradesh, in the Rayalaseema region); Meghalaya caves
Quartzite and resistant metamorphic rocks (quartzite is sandstone hardened by heat and pressure)	Ridges	The rock around them wears away, and the hard quartzite is left standing	Aravalli Range (Guru Shikhar, 1,722 m, the highest point); Delhi Ridge (the northern tip of the Aravalli)
Shale (soft, fine-grained)	Valleys and lowlands	Wears away easily	Valleys between quartzite ridges in the Cuddapah and Vindhyan basins

7. Rocks as heritage and building material

• Makrana marble (Rajasthan): marble is limestone changed by heat and pressure. Makrana marble was used for the Taj Mahal (Agra) and the Victoria Memorial (Kolkata).
• Vindhyan red sandstone: comes from the Dholpur–Karauli belt (Rajasthan) and nearby areas. It was used in the Red Fort, Fatehpur Sikri and many Mughal and modern buildings.
• Deccan basalt: carved directly into the cliff.
• Ellora Caves: Buddhist, Hindu and Jain cave temples near Chhatrapati Sambhajinagar (Aurangabad), Maharashtra. Includes the Kailasa temple, cut from one single rock.

• Elephanta Caves: on Gharapuri island in Mumbai harbour, Maharashtra.

• Mahabalipuram (Mamallapuram, Tamil Nadu): rock-cut temples and reliefs (carvings on rock faces) from the Pallava age, carved in granite and charnockite.

• Charnockite is a hard, dark, granite-like metamorphic rock that formed deep in the crust. It is named after Job Charnock, the founder of Calcutta, whose tombstone is made of it.

• Geo-heritage: GSI declares National Geological Monuments. These are sites of rare geological value, protected for study and public awareness. Examples:

• Eparchaean Unconformity (Tirupati area, Andhra Pradesh). An unconformity is a gap in the rock record, where much younger rock lies directly on much older rock.
• Natural Geological Arch, Tirumala Hills (Andhra Pradesh).
• Columnar basalt at St Mary's Island (Udupi, Karnataka).
• Lonar crater lake in basalt (Buldhana, Maharashtra).
• Laterite at Angadipuram (Kerala).

• Siwalik Fossil Park (Himachal Pradesh).

• Draft Geo-heritage Sites and Geo-relics (Preservation and Maintenance) Bill, 2022: released by the Ministry of Mines.

• It would give GSI the power to declare and protect geo-heritage sites and geo-relics (fossils, rocks and specimens of geological value).
• It is still a draft and has not been passed into law (check the current status).

Prelims Hooks

• Chota Nagpur Plateau (Jharkhand) = "storehouse of minerals". Its metallic ores sit in Archaean–Dharwar rocks.
• Gondwana rocks = coal (Damodar, Mahanadi, Godavari valleys). Tertiary rocks = oil, gas and lignite (Neyveli, Tamil Nadu). Quaternary alluvium = almost no minerals.
• Parent rock to soil: basalt → black soil; granite and gneiss → red soil; leaching in wet tropics → laterite and bauxite; river deposits → alluvial soil.
• Borra Caves and Belum Caves are limestone karst caves. Both are in Andhra Pradesh, not Telangana or Odisha.
• Hampi (Karnataka) granite tors; Delhi Ridge = quartzite at the northern end of the Aravalli; Deccan basalt = step-like trap plateaus.
• Ellora and Elephanta are carved in basalt. Mahabalipuram is carved in granite and charnockite. Makrana = marble (Rajasthan).
• India's critical mineral list (2023) has 30 minerals. 24 of them are in Part D, First Schedule of the MMDR Act, 1957, so the Centre auctions them [2][3].
• NCMM (January 2025): runs 2024-25 to 2030-31, outlay ₹16,300 crore, with 1,200 GSI exploration projects [2][3].
• Lithium in Reasi (J&K, February 2023) was reported as an inferred resource. It is not a proven reserve. This is a common trap in options.

Mains Points

• Rock type explains India's mineral map (GS-I/III):
• Metallic ores are packed into the Peninsular shield (the Jharkhand–Odisha–Chhattisgarh–Karnataka belt), coal into Gondwana troughs, and oil and gas into Tertiary basins (Assam, Gujarat, Mumbai High).

• So mining, steel plants and thermal power plants cluster on the plateau, while the alluvial plains feed people through farming. This shapes where industries locate, and the tribal displacement and conflict in mineral belts.

• Critical minerals and energy transition (GS-III):

• Demand for lithium, cobalt, nickel and REE is rising fast, and India imports most of them.
• Policy response: the 30-mineral list (2023), central auction powers under the MMDR Act, and the NCMM (₹16,300 crore, 2024-25 to 2030-31). The mission aims at domestic exploration, overseas sourcing (KABIL: Khanij Bidesh India Limited) and recycling [2][3].

• The Reasi lithium find shows that early-stage resources need more exploration before they can be mined.

• Parent rock, climate and soil management:

• Black soils hold water but crack, and they need careful irrigation.
• Red and laterite soils are leached and acidic, and they need lime and manure.

• Bauxite mining on laterite plateaus (Odisha's Niyamgiri, the Eastern Ghats) puts minerals against soil, water and tribal rights.

• Geo-heritage conservation (GS-I culture / GS-III environment):

• Sites like Lonar crater, St Mary's Island basalt and fossil parks face quarrying, building and vandalism, and no law yet protects them.
• The draft Geo-heritage Bill, 2022 could fill this gap. It also supports geo-tourism and earth-science education.