Coal: formation, grades and the Gondwana-Tertiary divide

Detail

Why coal matters in India's energy mix

• Coal is a fossil fuel. It is a black or brown rock that burns, made from plants that died millions of years ago.
• Coal gives about 55% of India's primary commercial energy (the energy bought and sold as fuel). About 72% of India's electricity comes from coal (IMYB 2022) [3].
• India has mined coal commercially since 1774. Coal mines were nationalised on 01.05.1973 (taken over by the government) [3].
• Production in 2024-25: 1,047.52 million tonnes (MT), 4.98% more than the year before. The target was 1,080.20 MT [2].
• Coal India Limited (CIL): 781.06 MT
• SCCL (Singareni Collieries, Telangana): 69.01 MT

• Captive and other mines: 197.46 MT [2]

• World position (2021): China produced about 50% of the world's coal and lignite. India was second at 9.0%, then the USA (7.88%), Indonesia (7.80%) and Australia (6.02%) [3].

How coal forms (step by step)

• Cause: plants grow thickly in swamps. When they die, they sink into wet, airless mud and do not fully rot.
• Process:
• More layers of mud and sand pile on top. The plant mass is pressed down and buried deeper.
• Deeper down it gets hotter and the pressure rises. Water and gases are squeezed out, so the share of carbon goes up.

• The longer and deeper the burial, the more "mature" the coal becomes. Experts call this organic maturity (how far heat, pressure and time have changed the plant material) [3].

• Result: the grade of coal depends on how hard it was pressed, how deep it was buried and for how long.

• The full sequence: peat → lignite ("brown coal") → sub-bituminous → bituminous ("hard coal") → anthracite [3].

Grades of coal (lowest to highest carbon)

Grade	What it is	Carbon / moisture / heat	Where in India
Peat	Half-rotted swamp plants. The first stage of coal	Low carbon, high moisture, little heat	Not a commercial fuel
Lignite	Soft brown coal. Its colour ranges from brown to dark black [3]	High moisture, low-to-medium heat	Neyveli (Tamil Nadu), Puducherry, Kutch and Bhavnagar (Gujarat), Barmer and Bikaner (Rajasthan), J&K
Sub-bituminous	The stage between lignite and bituminous coal [3]	Medium	—
Bituminous	Formed by deep burial at higher temperatures. Harder and blacker. The most common commercial coal	High carbon, good heat	Gondwana coalfields (Jharkhand, Odisha, Chhattisgarh, West Bengal, Madhya Pradesh, Telangana)
Anthracite	The best hard coal. Burns with almost no smoke	Highest carbon, highest heat	Very little in India, mainly Jammu and Kashmir

• Coking coal (metallurgical coal): high-grade bituminous coal. When heated without air, it turns into coke (a hard, porous fuel). Coke is used in blast furnaces (tall furnaces that smelt iron ore into iron).
• India's coking coal resources are graded as prime coking 5,443.41 MT, medium coking 30,132.09 MT and semi-coking 1,797.48 MT (as on 01.04.2025) [2].
• All coking coal comes to 37,372.98 MT, only about 9.3% of all coal resources [2]. It is found mainly at Jharia (Damodar valley, Jharkhand).

• Why India imports it: the steel sector and coke makers import coking coal because there is not enough at home and home coal is poorer in quality. Coal imports are allowed freely under Open General Licence (no special permit needed) [3]. Much of the imported coking coal comes from Australia.

• Non-coking coal: used mostly in thermal power stations (which burn coal to make steam and electricity) and in cement and sponge-iron plants.

• Gondwana non-coking resources: 3,61,647.82 MT, about 90% of the total (01.04.2025) [2].

• (NCERT: about 80% of Indian coal is non-coking.)

• Grades G1–G17: non-coking coal is graded by heat value. In the 01.04.2025 inventory:

• Superior grades (G1–G6): only 40,328.72 MT
• Inferior grades (G7–G17): 2,93,130.31 MT, about 73% of all coal [2]

Ash: the main quality problem

• Ash is the rock and mineral matter left behind after coal burns. More ash means less heat, more fly-ash waste and more wear on boilers.
• Indian Gondwana coal is high-ash, often 30–45%.
• Raw coal sent to washeries: ash content of 24% to 33%. (A washery is a plant that cleans coal to remove ash.) [3]
• After washing:
• Washed coal: 19–22% ash
• Middlings (the medium-quality part): 35–40% ash

• Rejects: over 50% ash [3]

• Why the ash is so high: the plant material was mixed with river mud and sand as it settled in Gondwana basins. That mineral matter stayed in the coal.

The Gondwana-Tertiary divide

Feature	Gondwana coal	Tertiary coal
Age	About 250–300 million years (Permian period) (NCERT Class 10: "a little over 200 million years")	About 15–60 million years (NCERT Class 10: about 55 million years)
Share of resources	3,99,020.80 MT, about 99.6% of 4,00,715.45 MT (01.04.2025) [2] (NCERT: about 98%)	1,694.65 MT, about 0.4% [2]
Type	Mostly bituminous. Includes all of India's coking coal	Lower carbon. All of it is classed as "high sulphur" coal [2]
Quality	High ash, low sulphur	Low ash and high heat value, but high sulphur. So it cannot be used directly as metallurgical coal [3]
Region	Eastern and central Peninsular India, along river valleys. A little also in Assam and Sikkim [3]	Assam, Arunachal Pradesh, Nagaland, Meghalaya [3], and Kalakot (J&K)

Gondwana coal

• Gondwana coal formed in Gondwanaland (the old southern super-continent that included India, Africa, Australia, South America and Antarctica). The coal formed in long, sunken troughs along old river valleys.
• Main river-valley belts:
• Damodar valley (Jharkhand–West Bengal): Jharia (largest coalfield; coking coal), Raniganj (second largest), Bokaro, Giridih, Karanpura
• Mahanadi valley (Odisha): Talcher and Ib Valley, mined by MCL (Mahanadi Coalfields Ltd) [3]
• Son valley: Singrauli (Madhya Pradesh–Uttar Pradesh border)

• Godavari and Wardha valleys: Telangana and Maharashtra. SCCL in Telangana produces non-coking coal and supplies most of South India's coal users [3]

• Resources by state, highest to lowest (01.04.2025) [2]:

Rank	State	Resource (MT)
1	Odisha	1,00,975.78
2	Jharkhand	93,254.06
3	Chhattisgarh	85,263.22
4	West Bengal	34,386.09
5	Madhya Pradesh	33,563.62
6	Telangana	23,288.62
7	Maharashtra	13,586.70
8	Bihar	9,353.44

• How certain the estimates are (01.04.2025) [2]:
• Total: 4,00,715.45 MT, up to 1,200 m depth, counting only seams 0.90 m or thicker
• Measured: 2,20,412.35 MT (about 55%)
• Indicated: 1,49,048.07 MT
• Inferred: 30,506.45 MT, plus 748.58 MT from mapping
• The inventory is prepared by the Geological Survey of India (GSI) from data of CMPDI, MECL, GSI, SCCL and other agencies.

Tertiary coal and the North-East

• Tertiary coal is much younger. It formed in the Tertiary period (about 66 to 2.6 million years ago), mainly in coastal swamps of the North-East. It has less carbon and more sulphur. Sulphur makes the coal corrosive, and burning it releases sulphur dioxide (a cause of acid rain).
• Main fields:
• Meghalaya: Darangiri, Cherrapunji, Mewlong, Langrin
• Upper Assam: Makum, Jaipur, Nazira
• Arunachal Pradesh: Namchik-Namphuk

• Jammu and Kashmir: Kalakot

• Resources by state (01.04.2025) [2]:

State	Resource (MT)
Meghalaya	583.22
Assam	525.01
Nagaland	510.21
Arunachal Pradesh	90.70

• NEC (North Eastern Coalfields, part of CIL) runs three mines: Tirap, Tikak and Tipong. Tipong is underground; the other two are opencast [3].

Rat-hole mining in Meghalaya

• Rat-hole mining means digging very narrow tunnels, often barely wide enough for one person, to reach thin coal seams. In Meghalaya it is often done by families.
• Why it happens: Meghalaya's Tertiary coal seams are thin, so large machines are not worth using. Small, narrow pits are cheaper.
• Where: Jowai (Jaintia Hills) and Cherrapunjee (East Khasi Hills).
• Harms:
• The tunnels are unsafe and can flood or collapse.
• Children have been used as workers.

• Acid water drains from the mines and makes rivers acidic.

• Ban: the National Green Tribunal (NGT) banned rat-hole mining in 2014.

Lignite

• Lignite is found in Tertiary rocks in the southern and western parts of the Peninsula, and also in J&K and Odisha [3].
• Total resources: about 47,370.54 MT (01.04.2025) [2].
• Resources by state, highest to lowest (01.04.2025) [2]:

Rank	State/UT	Resource (MT)
1	Tamil Nadu	37,523.65 (about 79%)
2	Rajasthan (Barmer, Bikaner)	6,661.17
3	Gujarat (Kutch, Bhavnagar)	2,722.05
4	Puducherry	416.61
5	Jammu and Kashmir	27.55
—	Kerala	9.65
—	Odisha	5.93
—	West Bengal	3.93

• Neyveli lignite (Cuddalore district, Tamil Nadu) is the largest lignite deposit in India.

• The Neyveli Lignite Mine is the largest opencast mine in the country [3]. (Opencast means the coal is dug from an open pit at the surface, not from tunnels.)

• NLC India runs three opencast mines at Neyveli and one at Barsingsar (Rajasthan). Their total capacity is 30.60 million tonnes per annum (MTPA) [3]:

• Mine-I: 10.5 MTPA
• Mine-IA: 3.0 MTPA
• Mine-II: 15.0 MTPA

• Barsingsar: 2.1 MTPA

• Pithead power stations are power plants built right next to the mine.

• Why: lignite is wet and bulky, so it is costly to carry far.

• So: it is burnt close to the mine, and electricity, not fuel, is sent out.

• Production: India mined 28.32 MT of lignite in 2025-26 (up to December 2025). NLC mined 14.45 MT of this, and Barmer Lignite (BLMCL) 4.07 MT [2].

• Neyveli lignite is the only notable fuel in the south-western mineral belt (Karnataka, Goa, Kerala, Tamil Nadu uplands).

Prelims Hooks

• Grades by carbon, lowest to highest: peat → lignite → sub-bituminous → bituminous → anthracite. Anthracite in India: mainly Jammu and Kashmir.
• Gondwana coal is about 99.6% of India's coal resources (4,00,715.45 MT, 01.04.2025). Tertiary coal is only 1,694.65 MT and is all classed as high sulphur [2].
• Coal resources by state, highest first (01.04.2025): Odisha > Jharkhand > Chhattisgarh > West Bengal > Madhya Pradesh [2].
• Coking coal is only about 9.3% of resources. It is found mainly at Jharia (Damodar valley, Jharkhand) [2].
• Field–state pairs: Darangiri, Mewlong, Langrin → Meghalaya. Makum, Nazira → upper Assam. Namchik-Namphuk → Arunachal Pradesh. Kalakot → J&K.
• Trap: North-East Tertiary coal is low-ash and high in heat value, but its high sulphur keeps it from being used directly as metallurgical coal [3].
• Lignite: Tamil Nadu holds about 79% of resources. Then come Rajasthan, Gujarat and Puducherry [2]. Neyveli is in Cuddalore district and is India's largest opencast mine [3].
• Rat-hole mining (Jowai, Cherrapunjee, Meghalaya) was banned by the NGT in 2014.
• Coal production in 2024-25: 1,047.52 MT, the first year above 1 billion tonnes. CIL mined 781.06 MT of it [2].

Mains Points

• Distribution pattern (GS-I): about 99.6% of coal lies in Gondwana basins of the Damodar, Mahanadi, Son and Godavari–Wardha valleys, in the eastern-central Peninsula [2][3].
• So: steel and thermal power plants cluster in the Chota Nagpur–Odisha belt.

• Also: the North-West and South depend on long-distance rail transport of coal, or on local lignite such as Neyveli and Barmer.

• The quality problem (GS-III): India has huge resources, but 73% are inferior grades (G7–G17) and coking coal is only about 9.3% [2]. Raw coal ash runs at 24–33% [3].

• So: India imports coking coal for steel, mostly from Australia.

• Response: coal washeries and blending to stretch home supplies [3].

• Environment and people (GS-III): Tertiary coal is high in sulphur, which raises sulphur dioxide pollution.

• Rat-hole mining in Meghalaya makes rivers acidic and costs lives. This led to the NGT ban of 2014.
• High-ash Gondwana coal leaves huge piles of fly ash.

• These problems explain why India is shifting towards non-fossil capacity, even though coal still generates about 72% of electricity [3].

• Energy security: coal is India's main home-grown fuel and will remain central for many years.

• Pithead power (generating at the mine, like Neyveli) cuts transport costs.
• Captive mines (mines that supply the owner's own plants) grew 28% in 2024-25 [2].