The rock formed from compacted plant remains is called coal. Coal is a sedimentary rock that forms from the accumulation and transformation of plant material, mainly in swampy environments where organic material becomes buried under layers of sediment. Over millions of years, heat and pressure convert these plant remains into various types of coal, ranging from lignite (brown coal) to anthracite (hard coal). Coal has historically been a significant energy source for electricity generation and industrial processes, but its use has raised environmental concerns due to carbon emissions and other pollutants associated with its combustion.