The dendritic markings on this thin slab of limestone look like a fossil of a delicately branching sea fan, but this is not a fossil. It is a natural mineralogical formation that was created when waters rich in iron and manganese (also called psilomelane) infiltrated the microscopically thin space between layers of pale tan limestone. The stunning patterns on this specimen, which are colored a chocolate brown with red highlights, make this an interesting and attractive specimen of the unusual mineralogical formation called dendrites.