A forest becomes petrified or turned to stone under certain conditions, through the action over the centuries of water containing large quantities of minerals.
Tree trunks buried ages ago under mud, sand or volcanic ash have been gradually transformed as water seeped into the empty cells of the decaying wood, filling them with mineral matter and preserving every detail of the original structure.
Petrified forests have been found in many parts of North and South America, dating from different geological periods and containing stone replicas of the trees that grew in those eras. The most famous of these forests is the Petrified Forest National Park in north Arizona, in the United States. There thousands of stone trunks and logs have been exposed to view through the rain washing away the soil in which they were buried. Although now composed of a mineral called silica, the original details of the trees can be studied through a microscope. Some of the trunks are up to 80 feet long and three to four feet in diameter. They are the fossils of cone-bearing trees belonging to Triassic times, the age of the dinosaurs, and are more than 150 million years old.