Answer:
coal
Peat
Bituminous
Anthracite
Explanation:
Peat is the first step in coal formation. Peat is composed of over 60% organic matter; typically, ferns and vegetation found in swamps or bogs. As a result of the high water content of this environment, peat contains a lot of water, which limits its heat content or the amount of energy it contains. It's a very soft brown coal.
Bituminous coal is formed as more pressure is applied to lignite coal. The greater the pressure applied, the more water is expelled, which increases the amount of pure carbon present and increases the heat content of the coal. Bituminous coal is often classified as sub-bituminous or bituminous. The difference is that sub-bituminous is the transition stage from lignite to bituminous coal. Bituminous coal is widely used in the United States and across Europe.
Anthracite coal is a metamorphic rock and is considered the highest grade coal. It's hard and dark black in color. It has a very light weight when compared to other forms of coal, as there is very little water present in anthracite. As a result, anthracite has the highest heat content. Anthracite is formed when bituminous coal is subjected to great pressures, such as those associated with the folding of rock during the creation of mountain ranges.
coal is just well...coal :3
