A stunning example of an iridescent ammonite fossil of the species Caloceras johnstoni from North Somerset, UK.
The piece of thin limestone matrix measures 128 mm (5.1 inches) across and contains a single ammonite that measures 38 mm (1.5 inches), making it a juvenile of this species.
The ammonite is very well preserved and has been prepared out of the rock to reveal the shell, which displays some stunning iridescent colours that change depending on the angle that the fossil is viewed at. There is a beautiful mix of red, gold, and orange colours in the shell - making some of the strongest colours possible in these fossils. It weighs 225 grams.
It is an unusual example as it has a bivalve shellfish resembling an oyster that attached itself to the shell either in life or after the ammonite died and the shell came to rest on the seafloor. The bivalve has taken the shape of the ammonite's whorls as it grew on it. A real snapshot of life in the Jurassic oceans.
Around 200 million years old (Hettangian, Early Jurassic), this fossil would make a wonderful addition to any collection. These fossils are preserved in the same way as the more famous Canadian "ammolite", which is turned into valuable gemstones due to the stunning iridescence.