Information on Petrified Fossils

Basics

• Petrifaction, the process by which specimens are petrified, is a relatively rare method of fossilization. Like permineralization, a more common process, petrifaction turns organic material to stone. However, unlike permineralization, where the porous spaces in bone and organic matter are filled with minerals, the entire structure of the fossilized specimen is replaced with minerals. Though all organisms can be petrified, from bacteria to vertebrates, the most famous examples are usually in the form of petrified wood.

Petrified Wood

• In petrified wood, all, or nearly all, of the organic matter has been replaced with minerals, most often quartz or other types of silica, while simultaneously keeping the basic structure of the wood intact. Petrifaction occurs underground after the wood has been buried by sediment. Groundwater, which is rich in minerals, flows through the sediment and deposits its minerals in the cells of the wood. As the plant's cellulose and lignin decay, the minerals stay put, and eventually form a complete mold of the specimen. This process can occur in mass, with forests of petrified wood known, predictably, as petrified forests.

Coloration

• Several elements found in the water that contributes to the creation of petrified wood factor into giving the specimens unique colorations and patterns. The silica that makes up the fossil is in itself colorless, but when the source water is contaminated with various elements, it adds hues of color. Carbon creates black; cobalt, chromium and copper create green or blue, iron oxides create browns, reds, and yellows; manganese creates pink or orange; and manganese oxides create black or yellow.

Artificial Petrifaction

• The process of petrifaction has been successfully simulated and demonstrated within laboratories. Small cubes of pine are soaked in an acid bath for 48 hours, after which it is soaked in a silica solution and then finally cooked at a temperature of 1,400 degrees C in an argon atmosphere. The process results in silica carbide petrifaction. It can be repeated, with a similar result, using tungsten instead of silica, resulting in tungsten carbide petrifaction.

Rhynie Chert

• Found in Scotland, the Rhynie chert is one of the most famous examples of large-scale petrifaction in the world. It contains numerous examples of fossilized plant, fungal, lichen and animal life dating back about 410 million years ago, dating it in the early Devonian. This formation is so well fossilized that even microscopic details, like cell walls, are clearly visible.