How Does Petrified Wood Form

How Does Petrified Wood Form?


The magnificent petrified trees in the forests of Arizona, what happened to wood that made it this way? They say that petrified wood is so old that these came from the era of the dinosaurs. But do you know how petrified wood was made? This guide will show you how.

What is petrified wood and how is it formed?

Petrified wood is considered a fossil which means it was formed when the plant material is buried by sediment. When wood is buried deep in the muck it is protected from decay brought about by the exposure to oxygen and organisms.

And as wood is preserved in deep water, the minerals in groundwater flow through the sediment, replacing the original plant material like silica, calcite, and pyrite. There are even very expensive minerals that can infiltrate wood like opal. The result is a fossil made from the original woody material that often exhibits preserved details of the tree bark, wood, and cellular structures.

Petrified wood all over the world

Petrified Forest National Park

This is possibly the most popular petrified parks in the world. The Petrified Forest National Park near Holbrook in northeastern Arizona has formed millions of years ago. About 225 million years ago, this was simply lowland that has a tropical climate with a dense forest.

Rivers made by tropical rainstorms washed mud and other sediments. This was where you would find giant coniferous trees 9 feet in diameter and towering 200 feet lived and died. Fallen trees and broken branches from these trees were buried by rich river sediments. Meanwhile, volcanoes nearby erupted numerous times and the ash and silica from these eruptions buried the area.

Eruptions caused large dense clouds of ash that buried the area and this quick cover prevented anything from escaping and of course, nothing can also move in, even oxygen and insects. In time, the soluble ash was dissolved by groundwater through the sediments. The dissolved ash became the source of silica that replaced the plant debris. This silication process creates petrified wood. Aside from silica, trace amounts of iron, manganese and other minerals also penetrated wood and this gave petrified wood a variety of colors. This is how the lovely Chinle Formation was made.

So how was this area discovered? Millions of years after the Chinle Formation were created, the entire area was dug and the rocks found on top of Chinle have eroded away. What was discovered was wood here was much harder and resistant to weathering compared to the mud rocks and ash deposits in Chinle. Wood that was taken from the ground surface as nearby mud rocks and ash layers washed away.

The areas of the Park are covered with petrified wood trunks, branches, and fragments. Visitors that come to the park are not allowed to collect petrified wood in the park.They are only allowed to observe and take photos.

Australian Peanut Wood

Australian peanut wood is petrified wood. The name was from the wood’s white markings which are the size and shape of peanuts. The markings are actually boreholes made in the wood by a shipworm which is a tiny species of clam.

Other locations with petrified wood

Petrified wood can be found in volcanic deposits and sedimentary rocks at a variety of locations worldwide. This type of wood was usually found where volcanic activity covered plant material with ash and debris. You can find petrified wood where there are sedimentary deposits replaced by minerals coming from groundwater.

You will find these mostly around coal seams In the United States and some of the most noteworthy locations are the following:

  • Petrified Forest National Park near Holbrook, Arizona
  • Petrified Palm Deposits in the Catahoula Formation of Louisiana, Texas, and Mississippi
  • Ginkgo Petrified Forest near Wanapum Reservoir, Washington
  • The Petrified Forest near Calistoga, California
  • Mississippi Petrified Forest near Flora, Mississippi
  • The Gilboa Fossils near Gilboa, New York
  • Florissant Fossil Beds near Florissant, Colorado
  • Gallatin Petrified Forest near Yellowstone, Wyoming
  • Escalante Petrified Forest State Park near Escalante, Utah
  • Petrified Wood Park in Lemmon, South Dakota


Petrified wood is considered a fossil. It was formed when the plant material is buried by sediment and infiltrated by silica-rich groundwater.There are a number of petrified wood forests all over the world but the most popular is the Petrified Forest National Park in Holbrook, Arizona where lovely petrified trees abound.  

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