Which of the following correctly depicts the progressive metamorphism of coal and its effect on the increase in rank?
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A.
Peat → Lignite → Bituminous coal → Anthracite → Graphite
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B.
Lignite → Peat → Bituminous coal → Anthracite → Graphite
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C.
Lignite → Bituminous coal → Peat → Anthracite → Graphite
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D.
Peat → Lignite → Anthracite → Bituminous coal → Graphite
Correct Answer:
A. Peat → Lignite → Bituminous coal → Anthracite → Graphite
Explanation:
The correct sequence for the progressive metamorphism of coal is Peat → Lignite → Bituminous coal → Anthracite → Graphite.
Coalification is a metamorphic process where organic matter undergoes physical and chemical transformations due to increasing temperature, pressure, and time, typically resulting from deeper burial within the Earth's crust. This progression is categorized by rank, which reflects the degree of maturity the coal has reached.
The process begins with peat, a precursor to coal formed from decaying vegetation. As it is buried and subjected to heat and pressure, it transforms into lignite (low-rank brown coal), then into bituminous coal (middle-rank), and eventually into anthracite (high-rank coal). Under extreme metamorphic conditions, such as intense heat from tectonic activity or magma intrusions, anthracite can further transform into graphite, which represents the highest stage of this progression. As the rank increases, the carbon content and energy density of the material rise, while the moisture and volatile matter decrease.
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