Initially
the peat is converted into lignite or 'brown coal' - these are
coal-types with low organic maturity. In comparison to other coals,
lignite is quite soft and its colour can range from dark black to
various shades of brown.
Over many more millions of years, the continuing effects of temperature and pressure produces further change in the lignite, progressively increasing its organic maturity and transforming it into the range known as 'sub-bituminous' coals. Further chemical and physical changes occur until these coals became harder and blacker, forming the 'bituminous' or 'hard coals'.
Under the right conditions, the progressive increase in the organic maturity can continue, finally forming anthracite.
In addition to carbon, coals contain hydrogen, oxygen, nitrogen and varying amounts of sulphur. High-rank coals are high in carbon and therefore heat value, but low in hydrogen and oxygen. Low-rank coals are low in carbon but high in hydrogen and oxygen content. Different types of coal also have different uses.
Over many more millions of years, the continuing effects of temperature and pressure produces further change in the lignite, progressively increasing its organic maturity and transforming it into the range known as 'sub-bituminous' coals. Further chemical and physical changes occur until these coals became harder and blacker, forming the 'bituminous' or 'hard coals'.
Under the right conditions, the progressive increase in the organic maturity can continue, finally forming anthracite.
In addition to carbon, coals contain hydrogen, oxygen, nitrogen and varying amounts of sulphur. High-rank coals are high in carbon and therefore heat value, but low in hydrogen and oxygen. Low-rank coals are low in carbon but high in hydrogen and oxygen content. Different types of coal also have different uses.
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