We sometimes find fossils preserved by pyrite. They are prized as much for their pleasing gold colouring as they are for their scientific value as windows into the past. Sometimes folk add a coating of brass to increase the aesthetic appeal. Though this practice is frowned upon in paleontological communities.
Pyrite is a brass-yellow mineral with a bright metallic lustre. It has a chemical composition of iron sulfide (FeS2) and is the most common sulfide mineral. It forms at high and low temperatures usually in small quantities, in igneous, metamorphic, and sedimentary rocks. When we find a fossil preserved with pyrite, it tells us a lot about the conditions on the seabed where the organism died. If you'd like to see photos of fossils preserved in pyrite, head on over to the Fossil Huntress Blog ARCHEA at https://fossilhuntress.blogspot.com