There are a few clues that help in telling fossils from pseudofossils. Fossils need special conditions to be preserved, and that's why they're typically found in well-bedded sedimentary rocks made of fine-grained mud, looking like leaves pressed in the pages of a book. Objects in other types of rock usually aren't real fossils. Fossils have what I can only call an air of purpose: a shark's tooth clearly has its shape to perform a function. Even coprolites, fossilized feces, are that way. Pseudofossils fail that test either by being too well organized, like a crystal or a blank spheroid, or too unorganized. See how those clues apply to the set of common pseudofossils in this gallery.