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Difficulty: MediumRock Types, Formation, and Economic Importance

Coal is an economically vital rock widely utilized as a fuel source for power generation and industrial processes. Through which of the following processes is coal formed?

  1. A
    Thermal metamorphism of pre-existing calcareous rocks under high temperature
  2. Accumulation, decay, and compaction of organic plant remains in marshy environmentsAnswer
  3. C
    Rapid cooling and solidification of basaltic magma on the surface of the Earth
  4. D
    In-situ chemical weathering and downslope gravitational movement of surface minerals

Answer

The accumulation, decay, and compaction of organic plant remains in marshy environments over geological time.
Coal is an organically formed sedimentary rock derived from accumulated plant debris in swampy conditions. Over millions of years, heat and overburden pressure compress the organic layers, turning them into carbon-rich coal deposits.

Step-by-Step Solution

1
Identify the rock classification of coal.
Coal is categorized as an organically formed sedimentary rock.
Sedimentary rocks can be mechanically, chemically, or organically formed depending on the origin of the constituent materials.
2
Analyze the formation mechanism for organically formed sedimentary rocks.
Dense vegetation in swampy or marshy environments dies, accumulates in oxygen-poor conditions to prevent full decay, and undergoes compaction under overlying sediments.
Heat and pressure over millions of years convert peat into lignite, bituminous coal, and anthracite.
3
Select the option matching this organic sedimentary origin.
The correct response describes the decay, accumulation, and compaction of vegetative plant matter.
Igneous and metamorphic processes do not yield coal.

Key Concept

Organically Formed Sedimentary Rocks
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Topics

Rock Types, Formation, and Economic Importance

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