Origin and Definition of Coal

Introduction to Coal

• Coal is a fossil fuel and is often referred to as black diamond.
• It is a significant source of energy, especially in India where coal reserves are plentiful.
• Used in electricity generation, power plants, home consumption, and various industries.

Definition of Coal

• Coal is defined in geological terms as an organo-sedimentary rock.
  • Formed from the fossilized material of plants.
  • Not just imprints; coal results from dead plants being buried and protected from decomposition by sediment cover.

Composition of Coal

• Contains more than 50% organic matter.
• The rest consists of sediments and minerals.
• Substance with less than 50% organic matter is called organic shales rather than coal.

Formation of Coal

Key Processes

1. Deposition: Accumulation of plant material.
2. Preservation: Protection from decomposition by anoxic conditions (lack of oxygen).
3. Conversion: Over time, dead plant material is transformed into coal under specific conditions.

Factors Influencing Coal Formation

• Time: Sufficient duration is crucial for preservation.
• Pressure & Temperature: Driven by sediment layers above buried organic material.

Types of Coal

• Common classifications of coal:
  • Lignite (brown coal)
  • Bituminous (soft coal)
  • Anthracite (hard coal)
• Classification is based on the amount of carbon present.

Coalification Process

• The process of coal formation is called coalification.

Stages of Coal Formation

• Peat Formation:
  • First stage of coalification, occurs in swampy areas with anoxic environments where plant material is preserved.

Factors for Peat Formation

1. Evolutionary Development of Flora: Types of plants that evolved over geological time.
2. Climate: Influences growth and preservation of plants.
3. Geographical and Structural Position: Tectonic aspects of the region impact peat swamp formation.

Geological Time and Plant Evolution

Key Geological Periods

• Early Devonian: Growth of submerged plants (e.g., Silophytes).
• Late Early Devonian: Emergence of first land plants.
• Middle/Late Devonian: Rapid spread of land plants leading to thicker coal seams.
• Early Carboniferous: Significant and economically viable coal seams form.
• Late Carboniferous: Known as the Bituminous Coal Period; emergence of richer plant forests like Lepidodendrons and Sigillaria.
• Permian: Coal chiefly formed from gymnosperms (e.g., Chordates).
• Jurassic to Early Cretaceous: Continued presence of gymnosperms (e.g., ginkgophytes, cycadophytes).
• Late Cretaceous to Cenozoic: Dominance of angiosperms in coal formation.

Comparison of Flora

• Carboniferous Flora vs. Mesozoic/Cenozoic Flora:
  • Mesozoic and Cenozoic flora is more diverse and specialized compared to the less diverse Carboniferous flora.
  • The development of complex gymnosperms and later angiosperms during these periods increased biodiversity.

Summary

• Coal is a vital energy source formed through geological processes over millions of years.
• Understanding coal's definition, composition, formation, types, and the geological contexts of its development are crucial for studying energy resources and environmental science.