Organic Sedimentary Rocks
Organic sedimentary rocks form from the accumulation and lithification of organic debris, such as leaves, roots, and other plant or animal material. Rocks that were once swampy sediments or peat beds contain carbon and are black, soft, and fossiliferous. Rich enough in carbon to burn, coal is an organic sedimentary rock that is a widespread and important fuel source. Coquina, bioclastic limestone, and skeletal limestone are also technically organic sedimentary rocks but are usually grouped with the other limestones as being chemically precipitated.