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The coal found in Assam, Arunachal Pradesh, Nagaland and Meghalaya belongs to which geological type?
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Answer: Option D — Tertiary coal
Detailed Solution
The coal of north-eastern India, found in Assam, Arunachal Pradesh, Nagaland and Meghalaya, belongs to the Tertiary period. It is much younger than most of India's coal, being about 15 to 60 million years old.
Two main types of coal in India by geological age:
- Gondwana coal:
- It is about 250 to 300 million years old, formed in the Permian period.
- It makes up about 98 per cent of India's coal reserves and production.
- It is found in the river valleys of peninsular India, such as the Damodar (Jharkhand and West Bengal), Son (Madhya Pradesh), Mahanadi (Odisha and Chhattisgarh), Godavari (Telangana) and Wardha (Maharashtra).
- It is mostly bituminous coal of good to moderate quality, including coking coal.
- Tertiary coal:
- It is younger and of lower quality.
- It is found mainly in the north-east: the Makum coalfield (Margherita and Ledo) in upper Assam, the Namchik-Namphuk area of Arunachal Pradesh, the Garo, Khasi and Jaintia hills of Meghalaya, and parts of Nagaland.
- Smaller amounts occur in Jammu and Kashmir and the Himalayan foothills.
Characteristics of Tertiary coal:
It has a low ash content but a high sulphur content, which makes it unsuitable for many industrial uses without treatment. It tends to be brittle and friable.
It has a lower carbon content and heating value than Gondwana coal.
It is suitable for some uses in power generation, cement, tea processing and small industries, and is useful in the local economy.
The age of the Earth's periods (approximate):
- Carboniferous: 360 to 300 million years ago (when most of the world's coal formed, but not much in India).
- Permian (Gondwana in India): about 300 to 250 million years ago.
- Tertiary: about 66 to 2.6 million years ago.
Why not the other options?
- ✗Gondwana coal is the older, better-quality coal of peninsular India.
- ✗Carboniferous coal is common in Europe and North America, not in north-east India.
- ✗Precambrian rocks are too old to contain coal, since land plants had not yet evolved.
Quick tip
Remember: Gondwana coal = old, 98 per cent of India's coal (Damodar valley etc.); Tertiary coal = young, high-sulphur coal of the north-east (Makum, Meghalaya).
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Minerals & Energy Resources — Preparation
This question tests your understanding of Minerals & Energy Resources, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers India's mineral resources (iron ore, manganese, bauxite, copper, mica and others) and energy resources (coal, petroleum, natural gas, nuclear power and renewable energy), with their main producing regions, mines, oil fields and power plants. Questions often ask where a mineral is found, which state is the leading producer, or where an important power plant or oil field is located. For example, Jharia is known for coal, Digboi in Assam is the oldest oil field in India, and Tarapur in Maharashtra is the site of India's first nuclear power plant. Practise the minerals and energy resources questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.