A recent study found that many of the fossils from Germany’s Posidonia shale do not get their gleam from pyrite, commonly known as fool’s gold, which was long thought to be the source of the shine. Instead, the golden hue is from a mix of minerals that hints at the conditions in which the fossils formed. The discovery is important for understanding how the fossils — which are among the world’s best-preserved specimens of sea life from the Early Jurassic — came to form in the first place, and the role that oxygen in the environment had in their formation.