Mold fossils are impressions or hollow spaces left in rock where an animal or plant once existed but has since dissolved or decomposed. They form when the remains of an organism, such as a shell or plant, are buried in sediment and then decay, leaving a negative imprint of the organism's shape and surface features in the surrounding rock
. There are two main types of mold fossils:
- External molds : These capture the outer surface details of the organism, such as shell ridges or skin textures. When the original organism dissolves or is removed, the surrounding rock retains the external shape as a cavity
- Internal molds : These form when sediment or minerals fill the internal cavities of hollow structures like shells. After the shell dissolves, the filled sediment preserves the interior shape, sometimes called a steinkern
Mold fossils are typically hollow and represent a negative image of the organism. They often occur in sedimentary rocks and can provide important information about the size, shape, and surface features of ancient life forms, even when the original organism is no longer present
. Sometimes, minerals fill the mold, creating a cast fossil, which is a positive replica of the organism’s shape. Mold and cast fossils together help scientists reconstruct the appearance of ancient organisms and understand past environments
. In summary, mold fossils are natural imprints left in rock by organisms that have decomposed, preserving detailed external or internal shapes as hollow cavities in the sediment
