Fossilization: Difference Between Casts and Mold

The remains of an organism are often buried in the sediment and can then leave what is called a cast and a mold. If an organism decays away, it can leave the space that was once the organism which is the mold. If the mold is filled in, it then becomes a  cast. Hence, the casts and the molds are not the organisms themselves, but rather the 3-D imprints left behind.

Art:Fossil molds and casts preserve a three-dimensional impression of remains buried in sediment. The mineralized impression of the organism left in the sediment is called a mold. The mineralized sediment that fills the mold recreates the shape of the remains. This is called a cast.


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