Coal is best defined as a

Coal is best defined as a

• A. A renewable energy resource formed from sunlight.
• B. A metamorphic rock formed under high pressure.
• C. A combustible sedimentary rock. One example is Anthracite.
• D. A mineral used primarily as a fertilizer.

Answer: (C)

Coal is a combustible sedimentary rock formed from ancient plant material buried under sediments and transformed by heat and pressure over long geologic time. Through the process of coalification, peat from swampy forests becomes progressively denser and more carbon-rich, moving from lignite to bituminous coal and, at the highest rank, to anthracite. This higher carbon content is what makes it burn more cleanly and efficiently. Anthracite is a classic example of coal because it represents the high-rank end of this transformation: very hard, dense, and with a high carbon content, it burns with a strong, steady heat. That’s why coal fits the definition of a combustible sedimentary rock, and why anthracite is cited as an example. The other statements don’t fit as well: coal isn’t formed from sunlight, so it isn’t a renewable energy resource in that sense; it isn’t categorized primarily as a metamorphic rock in basic definitions (though anthracite is formed under more intense conditions and is often described in metamorphic terms); and it isn’t a mineral used as a fertilizer.

Coal is a combustible sedimentary rock formed from ancient plant material buried under sediments and transformed by heat and pressure over long geologic time. Through the process of coalification, peat from swampy forests becomes progressively denser and more carbon-rich, moving from lignite to bituminous coal and, at the highest rank, to anthracite. This higher carbon content is what makes it burn more cleanly and efficiently.

Anthracite is a classic example of coal because it represents the high-rank end of this transformation: very hard, dense, and with a high carbon content, it burns with a strong, steady heat. That’s why coal fits the definition of a combustible sedimentary rock, and why anthracite is cited as an example.

The other statements don’t fit as well: coal isn’t formed from sunlight, so it isn’t a renewable energy resource in that sense; it isn’t categorized primarily as a metamorphic rock in basic definitions (though anthracite is formed under more intense conditions and is often described in metamorphic terms); and it isn’t a mineral used as a fertilizer.