Common Pseudofossils

By Andrew Alden, About.com Guide

Liesegang ("LEEZ-gahng") bands or rings are curving lines or ribbons of dark-brown iron minerals that form in sandstones and some other rocks after the rock is lithified. They can be quite dramatic, but they aren't fossils. Their formation is not well understood. They are named for the German chemist Raphael Liesegang, who first described similar features in chemical experiments.