Coal is dark brown rock generated when land plants or aquatic plants are sufficiently heated and pressured after they are slowly piled up and buried in the water. Major component of coal is carbon. The International Coal Society defined in 1957 that coal should contain over 50% of carbon in weight or over 70% of it in volume. Depending on the extent of carbonization, coal is divided into peat, lignite, brown coal, bituminous coal and anthracite.
In the Orient, the term of ‘coal’ was recorded to be first used in the ‘Shuijing (水經)’ published in the age of the Three States in China. Its current term was finally coined after having been called by several terms since then. Along with the life of mankind, coal has such a long history, and myriad of scientists across the world have been discussing definition of coal over times.
- Coal is a mineralized object or mineralized fuel.
- Coal exists in earth crust in the form of strata which came mainly from hydrocarbon, and it is a solid matter that can be used as fuel for supplying heat or light.
- Coal is dense fossil of plants existing in strata that contains small amount of impurities.
- Coal is a combustible fossil of deposited and spoiled organisms that contains over 50% of ashes.
- As combustible carbon-contained rock that constitutes layers of deposited and decomposed cadavers of plants, coal can be used as fuel. So, the rock that cannot be economically used as fuel by containing much ash is not coal.
- Coal is the one that can be economically used among combustible rocks generated by sedimentation and decomposition of plants.
As stated above, there were varied theories on definition of coal in terms of content criteria, component or tissue of carbon. But the International Coal Society decided at its conference, which was held in 1957 in the United States, that ‘coal should contain over 50% of carbon in weight, and over 70% of it in volume’.
As dark brown and glossy mineral, coal is a solid matter that has specific gravity of 1.8 in physical aspect. And chemically, it is consisted of carbon component, water and ash. Major elements of coal include carbon, hydrogen and oxygen, and it contains relatively small amount of nitrogen and sulfur. In addition, it also contains tiny quantity of iron sulfide, magnesium carbonate and alkali chloride. In using coal as either fuel or raw material, these various components and elements have varied effects on handling, combusting or using it.