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What Is a Petrified Fossil?

Petrification is the process of turning living organic material into stone. This process takes place when the molecules in an organism are replaced with the molecules of a mineral. A petrified fossil is different from other fossils such as resin fossils or permineralized fossils because the original material of the organism is still intact in resin fossils or permineralized fossils. Permineralization is often confused with petrification because it is the first step in the petrification process. The difference is with permineralized fossils, the pores of the organism are filled with minerals but the tissue of the plant or animal are still intact and are not replaced with minerals.

Process
- The process happens when a living organism, such as a tree, gets knocked down and buried under sand and mud during a flood. The buried tree is cut off from oxygen, which prevents bacteria from rotting away the wood. Over time, water that contains a lot of sediment and minerals enter the pores of the tree. Eventually the water evaporates and crystals form from the minerals left behind in the tree. These minerals then start to replace the carbon compounds in the wood. Eventually all of the wood is replaced by minerals, according to author Gary Raham in his book "Fossils." This process can sometimes take between a few years to millions of years.
Minerals
- Calcite, iron, silica and copper are some of the most common minerals found in petrified fossils, although many types of minerals can petrify fossils. Some other types of minerals found in petrified fossils include gypsum, barite, flourite, hematite, galena, talc, uranium and sulfur. When these minerals come in contact with oxygen, they produce distinct colors in petrified fossils. Iron tends to create earth tones such as reds and browns. Copper creates green colors, and minerals like hematite create red and pink colors. The intensity of the color depends on the amount of the mineral in the organism.
Types of Petrified Fossils
- Petrified wood is the most common type of petrified fossil, but all living organisms can be petrified. One of the most common types of petrified animal fossil is petrified bone and teeth. Dinosaur bones are sometimes petrified after being buried for millions of years after mudslides and floods. These types of petrified fossil are less common than petrified wood because bone is more fragile and easily damaged by water and ice.
Rarity
- Petrification is a rare form of fossilization and isn't completely understood by scientists. Permineralization is a more common form of fossilization, especially with bone fossils, according to the National Computational Science in Education website. Many fossils do not complete the process of petrification and often stay permineralized. Fossils in general are rare because most living things tend to decompose too quickly after death to be preserved.

Nature