Some organisms, such as corals, often build a rigid framework which may be preserved pretty well intact when they get buried. Coal Coal is a sedimentary rock, that is not formed from minerals or other rocks. As time passes, the material gets buried deeper. A lot of pressure and heat are put on this material the deeper it is buried. Finally, this material becomes rock formed from the carbon in the vegetable matter.
Coal often shows fossil patterns of ferns and leaves from the original plants.
The final sediment may consist of one or more of the above three processes. Cache Creek Formation, British Columbia. Photo by Dirk Schmid. Fossils Fossils form in sedimentary rock when an animal or plant becomes buried in mud or sand before it is eaten or before it rots. If air is excluded, such as it would be in thick mud, over thousands of years the bones turn to stone by absorbing and exchanging minerals with the surrounding soil and water.