1. Peat Formation:
- The first stage begins with the accumulation of plant material, such as trees, ferns, and mosses, in swampy or marshy environments.
- As these plants die and fall, they form a thick layer of organic matter called peat.
- Peat is composed of partially decayed plant material with high moisture content.
2. Burial and Compaction:
- Over time, the peat layer becomes buried under layers of sediment, such as sand, clay, and silt.
- The weight of the overlying sediments compresses the peat, squeezing out water and initiating the coalification process.
3. Biochemical Alteration:
- As the peat is buried deeper, it undergoes biochemical alterations due to the activity of microorganisms.
- These microorganisms break down the cellulose and lignin, which are the main components of plant cell walls.
- The resulting products include humic substances, waxes, resins, and other organic compounds.
4. Coalification:
- With increasing depth and temperature, the biochemical changes accelerate, and the peat transforms into coal.
- The process of coalification involves the loss of water, oxygen, and other volatile components from the organic matter.
- The carbon content of the material increases, and the coal becomes denser and more compact.
5. Metamorphism:
- In the later stages of coalification, the coal may undergo further changes due to intense heat and pressure.
- This process is known as metamorphism, which leads to the formation of higher-rank coals, such as anthracite.
- Metamorphic coals have a higher carbon content, higher calorific value, and reduced moisture and volatile matter compared to lower-rank coals.
6. Maturation and Rank:
- The rank of coal is determined by its degree of coalification and reflects the extent of physical and chemical changes it has undergone.
- Coals are classified into various ranks, including lignite (brown coal), sub-bituminous, bituminous, and anthracite (hard coal), each with distinct properties and characteristics.
The overall process of coal formation can take millions of years, and the type and quality of coal produced depend on factors such as the composition of the original plant material, burial conditions, temperature, pressure, and geological history of the region.
