Imagine a time about 360 to 300 million years ago when the earth was covered with forests and swamps and the weather was hot and humid. This period is known as the Carboniferous period. The plants that died during this period were gradually covered by rocks and dirt. Buried under layers of sediment and subjected to heat and pressure over millions of years, the decaying plant matter led to the formation of coal. In essence, this means that coal is the energy of plants that died eons ago.

Coalification

The very slow process of coal formation occurs over millions of years and is called coalification. The process requires four essential conditions:

  • Abundant plant matter
  • Swampy, waterlogged environments
  • Burial under layers and layers of sediment
  • Sustained heat and pressure

Peat

Peat is the first step of Coalification. It is formed from plants that have partially decayed in marshy or waterlogged areas. It is a soft and fibrous organic material consisting of partly decayed plant and mineral matter with a high moisture content.

As the plant material continues to decompose further under the pressure of overlying sediments and lack of oxygen, it becomes drier and its carbon content increases, leading to different varieties of coal.

Lignite

Lignite is the second step in the coalification process. It is formed when Peat is subjected to heat and pressure under more accumulating layers of sediment above it. Lignite’s moisture content is high while its carbon content is low.

Bituminous

When Lignite is buried under even more layers of sediment and subjected to more heat and pressure, the coalification process leads to the third variety of coal called Bituminous coal.

Bituminous coal is a higher grade of coal than Lignite and has a lower moisture content and a higher carbon content. It is abundantly available in sedimentary rocks and is widely used for electricity and heat generation.

Anthracite

The final step of coalification leads to the formation of Anthracite which is considered the top quality of coal because it has the lowest moisture content and the highest carbon content. Anthracite is a harder form of coal and it has almost a metallic lustre. It also has the fewest impurities and the highest energy density.

Generally speaking, all four types of coal are found in coal mines in South Africa and around the world. South Africa, in particular, is known for its high quality of coal and is exported worldwide, generating tens of thousands of jobs not just in the mining industry but also in the shipping and logistics industries.

Coal Mining