Do the actual organism remains exist in a cast fossil? Or is it just filled with minerals, mud, etc?
In a cast fossil, the actual remains of the organism are usually not present. Instead, the fossil is formed when minerals, mud, or other substances fill the space left by the decayed organism, preserving its shape and creating a replica. This process occurs mainly in two ways: mold and cast formation.
First, when an organism such as a shell or bone is buried in sediment (like mud or silt) and eventually decays, it leaves behind an empty cavity called a mold. This mold then fills with minerals, sediments, or other materials that harden into a solid cast, replicating the shape of the original organism. The cast, therefore, is a fossilized copy of the organism but does not consist of its actual remains.
So, to answer your question, in a cast fossil, the actual organism remains do not exist. It is the void left by the organism's decay that gets filled with minerals, mud, or other substances to create the cast fossil.