This guide is intended for a novice to be able to tell the difference between various types of fossilized colonial corals. It is nearly impossible to be absolutely certain about an identification without taking thin slices of the fossil and viewing them under a microscope. Paleontologists often classify corals based on small differences that aren’t visible to the naked eye. Classifications also change as new paleontologists study them and have differing opinions on how they should be classified. So, the identifications in this guide are “best guesses” based on visible-to-the-eye characteristics.

I am in the process of expanding this from a focus on Petoskey Stones and am constantly making changes as I learn new information. Special thanks to the Polkadots for their patience with my endless questions.