Science, Tech, Math › Science Fossilized or Petrified: What's the Difference? Share Flipboard Email Print Chris M Morris/Flickr/CC BY 2.0 Science Geology Types Of Rocks Landforms and Geologic Features Geologic Processes Plate Tectonics Chemistry Biology Physics Astronomy Weather & Climate By Andrew Alden Geology Expert B.A., Earth Sciences, University of New Hampshire Andrew Alden is a geologist based in Oakland, California. He works as a research guide for the U.S. Geological Survey. our editorial process Andrew Alden Updated February 25, 2019 What's the difference between fossilized and petrified? It can be a little confusing. A fossil is any evidence of life that has been preserved in rock. Fossils include not just organisms themselves, but also the burrows, marks, and footprints they left behind. Fossilization is the name for a number of processes that produce fossils. One of those processes is mineral replacement. This is common in sedimentary and some metamorphic rocks, where a mineral grain may be replaced by a material with a different composition, but still preserving the original shape. What Makes It Petrified? When a fossil organism is subjected to mineral replacement, it is said to be petrified. For example, petrified wood may be replaced with chalcedony, or shells replaced with pyrite. This means that out of all fossils, only the creature itself could be fossilized by petrification. And not all fossil organisms are petrified. Some are preserved as carbonized films, or preserved unchanged like recent fossil shells, or fixed in amber like fossil insects. Scientists don't use the word "petrified" much. What we call petrified wood, they'd rather call fossil wood. But "petrified" has a nice sound to it. It sounds right for a fossil of something familiar that looks lifelike (like a tree trunk).