Common Pseudofossils

By Andrew Alden, About.com Guide

Concretions are probably the most common pseudofossils—certainly that's true of the "mystery rocks" that visitors bring to the Geology Forum. They are not fossils, although some concretions have fossils inside them. They take their shape from the formation of iron or carbonate minerals that act as a cement. Their shapes range from disks and balls to blobs and rootlike forms. See more examples in the Concretion Gallery.