Black fuel is a term used to describe combustible materials that are used as a source of energy. COAL and PEAT are two of the most common types of black fuel. COAL is a sedimentary rock composed of carbon, hydrogen, oxygen, nitrogen, and sulfur. It is formed from the remains of ancient plants and animals that have been compressed and heated over millions of years. PEAT is an organic material composed of partially decomposed plant matter. It is formed in wetlands and is often used as a fuel source in some parts of the world.