we found this in a band of washed up pebbles, shells and seaweed close to the sea line on Great Yarmouth beach in Norfolk. Not really sure whether it is a rock or a fossil but my young son is very keen to know.
One of the photographs has a ruler in for scale, although I'm not convinced they do the 'thing' justice, I would appriciate any help you can give me to find the identity of our mystery item. Thank-you.
This is a fossil sponge preserved in flint.
Flint is formed from a silica gel from the ancient sea floor, and often fossils were preserved in flint when the gel formed a nodule around them because of a chemical attraction to the dead organism. The silica gel later hardened into flint. As this sponge is preserved in flint we know that it is from the Late Cretaceous, 100-70 million years old, towards the end of the time of the dinosaurs.
Sponges are some of the most common fossils in flint. Sometimes the structure of the sponge is preserved inside the flint but usually the sponge skeleton breaks down and we are left with a hollow spherical flint nodule, known as a “rotten” flint. The fluffy texture that you can see here is a sign of a “rotten” sponge in flint and is the remains of the sponge that has broken down.
Sponges (Kingdom, Animalia; Phylum, Porifera) are animals that live attached to the sea floor. They don’t have mouths or any distinct organs. They pump water through their bodies and filter it to get small particles of food. Sponges have a fossil record that dates back about 600 million years, and there are about 10,000 species alive today. Some are very different to the sponges we use in the bathroom. Most live in the sea but some live in freshwater. They can be very bright colours, such as red, orange, yellow or even blue. Some can be giant, over several metres
I've attached a factsheet that explains more about how flint forms.
I hope this helps, and I hopw your son is happy he found a real fossil!