Coal is classified as which type of sedimentary rock?

Coal is classified as organic sedimentary rock because it forms primarily from the accumulation and compaction of plant material, particularly in swampy environments where plant debris can accumulate and be preserved over time. The process of forming coal involves the decay of plant materials in anaerobic (low-oxygen) conditions, leading to the production of peat, which over millions of years can transform into various types of coal as a result of increasing pressure and temperature.

In contrast, clastic sedimentary rocks are composed of fragments (clasts) of other rocks and minerals cemented together, while chemical sedimentary rocks are formed from the precipitation of minerals from solution often in water. Metamorphic rocks, on the other hand, originate from existing igneous, sedimentary, or older metamorphic rocks that have been transformed under heat and pressure but do not include coal. Thus, the unique process of formation and composition distinguishes coal as an organic sedimentary rock.