Iridescent Fossil Ammonites, Psiloceras planorbis, from England
SPECIES: Psiloceras planorbis
AGE: Lower Jurassic (198-201 million years)
LOCATION: Noth Somerset, England
FORMATION: Blue Lias Formation
This is an iridescent ammonite (Psiloceras planorbis) fossil from England. It has a naturally iridescent shell showing nice blues, greens and deep red colors. Like most fossils from the Blue Lias Formation, these ammonites have been compressed and flattened by the same geological processes of heating and pressure which gives them their iridescent shell.
Iridescent ammonites are reputed worldwide for their beautiful colorful glow. When the ammonite was alive, nacre was the main component of the shell: after the organism’s death, the shell fossilized over time to form aragonite. The iridescence can also contain many other minerals such as calcite and pyrite.
Ammoniteswere predatory mollusks that resembled a squid with a shell. These cephalopods had eyes, tentacles, and spiral shells. They are more closely related to a living octopus, though the shells resemble that of a nautilus. Ammonites appeared in the fossil record about 240 million years. The last lineages disappeared 65 million years ago at the end of the Cretaceous.