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How to Tell a Fossil From a Rock

Fossils form when the original minerals in the body of an animal or plant become trapped in sediment and decay. Other minerals that are compositionally similar to rocks replace these minerals. A fossil is a copy of a dead organism, but its chemical composition more closely resembles that of rock. It is no wonder, then, that fossils can be difficult to distinguish from rocks.

Things You'll Need

Fossil or rock
Computer
Internet
Magnifying glass

Instructions

- 1
  Find your specimen. You may already have an object that you think may be a fossil, or you may need to locate one. Should you want to go on a fossil-hunting expedition, search the web for sites in your area where fossils have been commonly found. It is more likely that you will find a fossil in a site where many fossils have been found than in a more random location.
- 2
  Go to a fossil identification web page. If you have gone to a geographical location where fossils are often found, see if that place has a corresponding website that allows you to compare what you found to what is commonly found in that location. For example, Shark River in New Jersey offers an identification page with pictures of various fossils that can be found there. Determine whether your specimen looks like any on the website. If it does, you are likely to have found a fossil rather than a rock.
- 3
  Look at an online fossil gallery to see whether the specimen you found matches any that can be seen online. This is a good idea if you haven't gone to a specific geographical location to find a fossil and are curious about whether you have a rock or a fossil. Use a magnifying glass to look closely at the specimen. If you do not look closely, you might mistake fossil patterns for those caused by normal rock erosion. For example, hemichordates, fossils that can be found on black shale, are particularly hard to recognize. Many fossils, though, have more identifiable patterns. For example, fossilized trilobites always have fragmented bodies and bilateral symmetry.
- 4
  Take your fossil to a museum to have a professional evaluate it. After you have done some of the preliminary work and are pretty certain you have a fossil rather than a rock, you can take your fossil to a museum that has a fossil identification day. During a fossil identification day, a professional can confirm that you have a fossil and help you locate more information about that fossil. The Museum of the Earth in Ithaca, New York, is one such museum that provides this service.

Rocks & Minerals