A stunning and perfect example of an iridescent ammonite fossil of the species Caloceras johnstoni from North Somerset, UK.
The matrix measures 380 mm (15 inches) across and the ammonite measures 148 mm (5.8 inches), which is huge for this species and as big as it gets. The shell sits in the original limestone matrix in which it was found that has been shaped for display. The ammonite is very well preserved and has been prepared out of the rock to reveal the shell, which displays some beautiful subtle iridescence with flashes of different colours appearing as the viewing angle changes.
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 2870 grams.
Around 200 million years old (Hettangian, Early Jurassic), this fossil would make a wonderful addition to any collection.