Petrified wood

Petrified wood is the remains, preserved in rock, of prehistoric trees. It is formed over thousands of years, as mineral-rich water seeps through the wood of a tree. The minerals in the water, such as calcium carbonate (CaCO3) and silica salts, either replace or enclose the tree's organic (living) matter and eventually harden into stone, in a process called petrification. Botanists (scientists who specialize in the study of plants) find these types of fossils to be very important since they allow for the study of the internal structure of extinct plants.

There are some instances in which the petrification of a tree is so complete that even the cellular structure of the tree is preserved. The best examples of this can be found in the Petrified Forest National Park in Arizona.