Fossil molds and casts preserve a three-dimensional impression of remains buried in sediment. Cast fossils occur when mold fossils are filled in with minerals that harden over time, creating a fossilized replica of the original organism. Mold fossil-A fossil formed when an animal, plant, or other organism dies and is covered by sediment, its flesh decays and bones deteriorate due to chemical reactions, and a cavity remains below the ground surface.
