A stunning example of an iridescent ammonite fossil of the species Caloceras johnstoni from North Somerset, UK.
The matrix measures 123 mm (4.95 inches) across and contains an ammonite that measures 81 mm (3.2 inches) across, which is large for this species. The shell sits in the original limestone matrix in which it was found that has been shaped and has a cut-flat base to allow it to stand freely by itself for display. The ammonite is very well preserved and has been prepared out of the rock to reveal the shell. The shell displays some beautiful subtle multi-coloured iridescence with different colours that appear as the viewing angle changes with green and orange colours against an overall pearlescent sheen. There is also a rare bivalve shell that attached itself to the ammonite when it was lying on the seafloor before being fossilised.
These fossils are highly sought after and very hard to find, especially complete like this. They are preserved in the same way as the famous Canadian "Ammolite" ammonites that are turned into valuable gemstones. The fossil weighs 245 grams.
Around 200 million years old (Hettangian, Early Jurassic), this fossil would make a wonderful addition to any collection.