A mold fossil is kind of like an impression that is made in the substrate. They are quite similar to the negative impressions left by an animal or a plant. Mold fossils are primarily formed through a process called ‘leaching.’
Cast fossils leave an imprint in the rock or sediment and go a single step further than the mold fossils.
These fossils are also called ‘ichnofossils,’ and they contain any potential information or traces left behind by the organism.