Coal is produced from the natural resource known as organic matter, primarily ancient plant material. Over millions of years, this organic matter undergoes a process of decomposition and transformation due to heat and pressure in the Earth's crust, resulting in coal formation. This process is known as coalification and takes place in three major stages: lignite, sub-bituminous, and bituminous coal, eventually leading to anthracite, the hardest and highest energy content type. Coal serves as a significant fossil fuel used for electricity generation and industrial processes worldwide.