Formation of Coal Prepared by: Izhar Mithal Jiskani – 09 MN 98
Formation of Coal
Coal is non-renewable fossil fuel formed in ecosystem where plant remain were preserved by
water and mud from oxidization and biodegradation. It can also be described as “Coal is the
compacted and preserved remains of plant matter and it is called a fossil fuel because it was
formed from the remains of vegetation that grew as long as 400 million years ago”.
It is readily combustible black or brownish-black rock and along with oil and natural gas it is one
of the three most important fossil fuels.
Coal is formed when accumulated plant debris is altered physically and chemically. The plant
debris such as leaves, barks, spores etc settled to the bottom of the swamp and decomposing
begins under the bacterial action. The decomposition is not complete because the stagnant water
in the swamps stops the decaying process due to the lack of oxygen. This partially decomposed
material is known as peat. Peat is the beginning of coal forming process and is called
Coalification.
There are four stages in coal formation: peat, lignite, bituminous and anthracite. The stage
depends upon the conditions to which the plant remains are subjected after they were buried - the
greater the pressure and heat, the higher the rank of coal. Higher-ranking coal is denser and
contains less moisture and gases and has a higher heat value than lower-ranking coal.
Coal is a sedimentary rock but the forms such as anthracite coal can be regarded as metamorphic
rocks because of later exposure to elevated temperature and pressure. It has a wide range of uses;
the most important use is for the generation of electricity.
Society of Mining Engineers,Department of Mining Engineers
Mehran University of Engineering & Technology, Jamshoro
Formation of Coal Prepared by: Izhar Mithal Jiskani – 09 MN 98
Theories associated with coal formation
1. The In-situ theory (Autochthanous)
The organic material from which the coal was formed; belongs to the site of deposition. Many
researchers have a strong objection on this theory as this specifies a reverse geological cycle but
the presence of plant roots under the floor of coal seam signifies the importance of this theory.
2. Drift Theory (Allochthanous)
The original vegetation material from which the coal deposit had been formed does not belong to
the site of deposition but transported by water to the present site. The supporters of this theory
have valid reasons to sustain; the most important one is that the coal is sedimentary rock, its
sediments brought down by erosion and deposited to low-lying areas of large water bodies and
covered with the other inorganic sediments.
Society of Mining Engineers,Department of Mining Engineers
Mehran University of Engineering & Technology, Jamshoro
