Photo of a pyritised ammonite fossil


Pyritised ammonite

Little pyritised ammonites from Gloucestershire in England, and around 190 million years old. They are a mixture of species, mostly Cheltonia, and vary slightly in size. The pyritisation is a natural process where the replacement is by iron pyrite instead of - say - quartz or calcite. The result is a silvery to brassy metallic sheen.