Which one of the following types of coal contains a higher percentage of carbon than the rest ?

1. Sedimentary Rocks and Organic Formation (basic)

To understand sedimentary rocks, imagine the Earth’s surface as a giant recycling machine. Unlike igneous rocks which form from cooling magma, sedimentary rocks are born from the debris of pre-existing rocks and life forms. This process begins with denudation—the wearing away of the Earth's crust by wind, water, and ice. These fragments, called sediments, are transported and eventually settle, usually in water bodies, in a process known as lithification (the compaction and cementation of sediments into solid rock) Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.171.

Because these sediments settle one on top of another over millions of years, the most striking feature of sedimentary rocks is their stratification or layering. These layers, or strata, can vary in thickness and are the reason why these rocks are often called stratified rocks Certificate Physical and Human Geography, The Earth's Crust, p.18. Crucially, because these rocks form at the surface under relatively cooler conditions, they are the primary home for fossils—the preserved remains of plants and animals trapped between layers during deposition.

While many sedimentary rocks are formed mechanically (like sandstone from sand grains), a fascinating sub-category is organically formed sedimentary rocks. These are born from the accumulation of organic matter rather than mineral debris. We generally classify them into two types based on their chemical dominance:

• Calcareous rocks: Formed from the skeletal remains of calcium-rich organisms like corals and shellfish (e.g., limestone, chalk) Certificate Physical and Human Geography, The Earth's Crust, p.19.
• Carbonaceous rocks: Formed from the highly compressed remains of heavy vegetation in swampy environments (e.g., coal) Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.172.

Sources: Physical Geography by PMF IAS, Types of Rocks & Rock Cycle, p.171-172; Certificate Physical and Human Geography, GC Leong, The Earth's Crust, p.18-19

2. Classification of Mineral Resources (basic)

To understand minerals, we first categorize them based on their chemical and physical properties. The most fundamental division is between Metallic and Non-metallic minerals. Metallic minerals are those from which metals can be extracted and are essential for the metallurgical industry, serving as the bedrock for industrialization and urban development Geography of India (Majid Husain), Resources, p.5. These are further subdivided into Ferrous (minerals containing iron, such as iron ore and manganese) and Non-ferrous (those without iron content, such as copper, bauxite, and gold) INDIA PEOPLE AND ECONOMY (NCERT Class XII), Mineral and Energy Resources, p.54.

On the other hand, Non-metallic minerals do not contain metals. These can be inorganic (like mica, limestone, and salt) or organic in origin. The organic non-metallic minerals are particularly significant because they form our Mineral Fuels or fossil fuels, such as coal and petroleum, derived from buried plant and animal life INDIA PEOPLE AND ECONOMY (NCERT Class XII), Mineral and Energy Resources, p.54. In the context of energy production, these resources are often categorized as Conventional (traditional sources like coal and natural gas) or Non-conventional (modern sustainable sources like solar, wind, and tidal energy) Contemporary India II (NCERT Class X), p.113.

Category	Sub-type	Examples
Metallic	Ferrous	Iron ore, Manganese, Nickel, Cobalt
	Non-Ferrous	Copper, Lead, Tin, Bauxite, Gold
Non-Metallic	Inorganic	Mica, Salt, Potash, Limestone, Graphite
	Organic (Fuels)	Coal, Petroleum, Natural Gas

When we look specifically at coal as a fuel mineral, it is classified based on its degree of "coalification" — the process of transformation from plant matter to mineral. This progression moves from Peat (low carbon, high moisture) to Lignite (brown coal), then Bituminous, and finally Anthracite, which is the highest-rank coal with the greatest carbon percentage (approx. 80–90%) and the least impurities Geography of India (Majid Husain), Energy Resources, p.2.

Sources: INDIA PEOPLE AND ECONOMY, TEXTBOOK IN GEOGRAPHY FOR CLASS XII (NCERT 2025 ed.), Mineral and Energy Resources, p.54; Geography of India (Majid Husain), Resources, p.5; Geography of India (Majid Husain), Energy Resources, p.2; Contemporary India II (NCERT Class X), Mineral and Energy Resources, p.113

3. Geological Distribution: Gondwana vs. Tertiary Coal (intermediate)

In India, coal is not just a uniform mineral; it is divided into two distinct geological categories based on when it was formed. Think of it like a vintage: the older the coal, the more time it has had to compress, lose moisture, and concentrate its carbon. This process, called coalification, defines the sharp contrast between Gondwana coal and Tertiary coal.

Gondwana Coal: The Ancient Powerhouse
Formed roughly 250 to 500 million years ago during the Permo-Carboniferous period, Gondwana coal accounts for about 98% of India’s coal reserves and nearly 99% of its production Geography of India, Majid Husain, Chapter 8, p.1. Geographically, these deposits are strictly associated with river valleys. The most significant is the Damodar Valley (spanning Jharkhand and West Bengal), which houses legendary fields like Jharia (the largest) and Raniganj India People and Economy, NCERT Class XII, Chapter 7, p.59. Other vital basins include the Sone, Mahanadi, and Godavari valleys. This coal is primarily Bituminous, meaning it is high-grade, low-moisture, and essential for heavy industries like steel smelting and thermal power.

Tertiary Coal: The Younger Relative
In contrast, Tertiary coal is a "geological youngster," formed much later (about 15 to 60 million years ago) during the Eocene to Miocene epochs Geography of India, Majid Husain, Chapter 8, p.6. Because it hasn’t spent as much time "cooking" under the Earth’s pressure, it is mostly Lignite or "brown coal." It is characterized by high moisture content and lower carbon (roughly 30–40%). Its distribution is also different; while Gondwana coal is found in the heart of the peninsula, Tertiary coal is found in the periphery—states like Tamil Nadu (Neyveli), Rajasthan, Gujarat, and parts of the Northeast like Assam and Meghalaya Geography of India, Majid Husain, Chapter 8, p.6-7.

Feature	Gondwana Coal	Tertiary Coal
Geological Age	~250–500 million years (Older)	~15–60 million years (Younger)
Primary Type	Bituminous & Anthracite	Lignite (Brown Coal)
Location Pattern	River Valleys (Damodar, Mahanadi, Sone)	Coastal & Extra-Peninsular (Neyveli, Assam)
Carbon Content	High (Good quality)	Low (Poor quality; high moisture)

Sources: Geography of India, Majid Husain, Chapter 8: Energy Resources, p.1, 6-7; India People and Economy, NCERT Class XII, Chapter 7: Mineral and Energy Resources, p.59

4. Industrial Applications: Coking vs. Non-Coking Coal (intermediate)

In the world of industrial minerals, coal isn't just a fuel; it is a critical raw material. The most important distinction for a UPSC aspirant to understand is between Coking Coal and Non-Coking Coal. This classification isn't just about how much heat they produce, but how they behave when subjected to intense heat in the absence of air. Coking Coal (also known as metallurgical coal) is the 'gold standard' for heavy industry. Its defining characteristic is its caking property: when heated in a closed oven without oxygen, it softens, becomes plastic, and eventually fuses into a hard, porous, and strong mass called coke Certificate Physical and Human Geography, GC Leong, Chapter 27, p. 265. This coke is indispensable in blast furnaces for smelting iron ore. It acts both as a fuel and a reducing agent, providing the structural strength to support the weight of iron ore and limestone inside the furnace while allowing hot gases to circulate through its pores. In India, our high-quality coking coal is largely found in the Damodar Valley (Jharkhand-West Bengal belt) and is essential for our massive steel plants like Durgapur Geography of India, Majid Husain, Chapter 8, p. 6. Non-Coking Coal, often called thermal or steam coal, does not have this ability to fuse into coke. When heated, it simply burns or turns into ash without softening. While it may still have high carbon content, its primary industrial application is power generation in thermal power plants and providing heat for cement and fertilizer industries. Most of India’s coal reserves belong to the Gondwana period, which provides us with vast amounts of bituminous coal. While much of this is high-quality, a significant portion is non-coking, requiring India to import high-grade coking coal to meet the specific needs of our metallurgical sector Geography of India, Majid Husain, Chapter 8, p. 1.

Here is a quick comparison to help you distinguish the two:

Feature	Coking Coal	Non-Coking (Thermal) Coal
Primary Use	Iron & Steel manufacturing (Metallurgy)	Electricity generation (Thermal power)
Behavior on Heating	Softens and fuses into a solid mass (Coke)	Does not fuse; remains as powder or ash
By-products	Releases volatile gases (coal gas, tar) to leave pure carbon	Burned directly for steam/heat

Sources: Certificate Physical and Human Geography, GC Leong, Chapter 27: Fuel and Power, p.265; Geography of India, Majid Husain, Chapter 8: Energy Resources, p.1; Geography of India, Majid Husain, Chapter 8: Energy Resources, p.6

5. Environmental Impact: Fly Ash and Carbon Emissions (exam-level)

Concept: Environmental Impact: Fly Ash and Carbon Emissions

6. The Coalification Process: From Peat to Anthracite (exam-level)

Coal is essentially a sedimentary rock of organic origin. The journey from a swampy forest to a hard, black mineral is a process called coalification (or carbonization). It begins when plant matter is buried in oxygen-poor environments, preventing complete decay. Over millions of years, as these layers are buried deeper, they are subjected to increasing geological pressure and geothermal heat. This process systematically drives out moisture and volatile gases, steadily concentrating the fixed carbon content. Consequently, the "rank" of coal is determined by its maturity—the further along it is in this process, the higher its carbon content and heating value.

The first stage is Peat, which is not yet true coal but a dark-brown, fibrous mass of partially decayed vegetation found in bogs Environment and Ecology, Majid Hussain, Chapter 9, p.9. As peat is compressed, it transforms into Lignite (or "Brown Coal"). Lignite is the lowest rank of actual coal, containing about 40–60% carbon and retaining significant moisture, which makes it smoky when burned Geography of India, Majid Husain, Chapter 8, p.1. In India, major lignite deposits are found in regions like Neyveli in Tamil Nadu.

With further burial and time, we reach the Bituminous stage. Known as "soft coal," this is the most abundant type globally and is highly valued in metallurgy and power generation because its moisture has been largely expelled Certificate Physical and Human Geography, GC Leong, Chapter 27, p.264. Finally, under intense pressure—often associated with mountain-building movements—we get Anthracite. This is the highest-rank coal, characterized by a metallic luster and a carbon content exceeding 80–90%. It burns with a short, blue, smokeless flame and leaves behind very little ash, making it the cleanest and most efficient variety, though it constitutes less than 5% of the world's total coal output Certificate Physical and Human Geography, GC Leong, Chapter 27, p.264.

Coal Type	Carbon %	Characteristics
Peat	<40%	High moisture; first stage of transformation.
Lignite	40–60%	Brown coal; high ash and moisture; smoky burn.
Bituminous	60–80%	Black coal; most common; used in smelting/industry.
Anthracite	80–95%	Hardest coal; highest heating value; smokeless.

Sources: Geography of India, Majid Husain, Chapter 8: Energy Resources, p.1; Environment and Ecology, Majid Hussain, Chapter 9: Distribution of World Natural Resources, p.9; Certificate Physical and Human Geography, GC Leong, Chapter 27: Fuel and Power, p.264-265

7. Solving the Original PYQ (exam-level)

This question tests your understanding of the coalification process, a core concept in economic geography. As you learned in the preceding modules, coal is formed through the progressive transformation of organic matter under intense heat and pressure over millions of years. This process, known as carbonization, results in the gradual expulsion of moisture and volatile matter, which systematically increases the fixed carbon percentage. To solve this, you simply need to identify which stage of this evolutionary ladder represents the most mature form of the mineral.

To arrive at the correct answer, apply the hierarchy of coal ranks you just studied. We begin with Peat, which is merely the first stage of transformation and contains high moisture with very low carbon. Lignite, or brown coal, follows as a slightly more compressed form. While Bituminous coal is the most common variety used in heavy industry, Anthracite sits at the absolute top of the quality pyramid. With a carbon content often exceeding 80–90%, it is the hardest and oldest form of coal, making (D) Anthracite the correct choice. According to Geography of India by Majid Husain, this high carbon density is exactly why it burns with a blue flame and leaves behind very little ash.

A common trap in UPSC geography is confusing economic abundance with chemical quality. Many students are tempted to pick Bituminous coal because it is the most abundant and widely used type in India's Gondwana deposits. However, the question specifically asks for the highest percentage of carbon, not the most commercially prevalent type. Always remember the progression: Peat → Lignite → Bituminous → Anthracite. As you move along this chain, moisture decreases while carbon concentration and heating value increase.