A stunning and large example of an iridescent ammonite fossil of the species Caloceras johnstoni from North Somerset, UK.
The matrix measures 185 mm (7.3 inches) across and the ammonite measures 150 mm (5.9 inches), which is huge for this species and about as big as they get. 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 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 iridescence with flashes of red and copper that appear as the viewing angle changes. There are also some small bivalve shells that encrusted the ammonite as it lay on the Jurassic seafloor. The back of the matrix has been coated in a rock-coloured plaster to make it stable.
These fossils are preserved in the same way as the famous Canadian "Ammolite" ammonites that are turned into valuable gemstones. The fossil weighs 960 grams.
Around 200 million years old (Hettangian, Early Jurassic), this fossil would make a wonderful addition to any collection.