* Formation: Coal forms from the accumulation and compression of plant matter, primarily in swampy environments. This process is a key characteristic of sedimentary rock formation. Over time, the layers of dead plant material build up, get buried under sediment, and experience pressure and heat, transforming into peat and eventually coal.
* Metamorphic Transformation: While coal is primarily sedimentary, it can undergo further transformation under intense heat and pressure. This process creates metamorphic coal, such as anthracite. Anthracite is a harder, denser, and more carbon-rich form of coal than bituminous coal. This transformation changes the composition and properties of the original sedimentary coal, making it a metamorphic rock.
In summary:
* Coal begins as a sedimentary rock: It forms from the accumulation and compression of plant matter.
* Metamorphic coal: When sedimentary coal experiences further intense heat and pressure, it transforms into a metamorphic rock.
Therefore, coal is not simultaneously both sedimentary and metamorphic. It starts as sedimentary, and under specific conditions, can become metamorphic.
