Petrified Wood: A Journey From Tree to Stone

By: Mark Mancini & Desiree Bowie  | 
petrified, wood
Petrified Forest National Park, located in northeast Arizona, is home to a number of animal and plant fossils. Here, you can see colorful crystal patterns are displayed in a cross-section of petrified wood. Arterra/Getty Images

Glen Rose, Texas, seamlessly intertwines its rich, prehistoric heritage with contemporary life, showcasing a landscape where dinosaurs once roamed amid lush vegetation. While the dinosaurs are long gone, some of their footprints and the fossilized remains of the ancient trees (also known as petrified wood) have been preserved.

You don't have to be a science buff to appreciate this ancient plant material. Indeed, as the people of Glen Rose learned, the fossils work nicely as a brick substitute. In the 1920s and 1930s, locals built numerous buildings using petrified wood, including a Prohibition-era speakeasy, which still stands. Let's explore the transformation of this highly sought-after plant material.


How Does Petrified Wood Form?

Petrified wood refers to a fossil formed when the organic components of woody plant material are gradually replaced by minerals, predominantly silica, via a process called permineralization. This process can only take place under the right set of circumstances.

When an organism dies, it usually decomposes. Such is the circle of life. The process that most people call "rotting" is a type of decay which sets in as microorganisms break down organic matter. Usually, a dead, fallen tree will be subjected to this process.


Once in a while, though, a newly deceased tree (or some other kind of woody plant) gets rapidly buried by mud, silt or volcanic ash. This blanketing material, or sediment, then shields the dead tree from oxygen. Because oxygen is the main driving force behind the decaying process, the smothered plant will begin to decompose far more slowly than it normally would.

Meanwhile, mineral-laden water or mud seeps into the dead tree's pores and other openings. As our plant's internal structure gradually breaks down, its organic material (wood fibers) gets replaced by silica and other minerals.

Over several million years, the minerals that replace the organic material gradually crystallize, forming a rock-like structure. This resulting structure may closely mimic the shape and internal features of the original tree, effectively preserving its essence in stone for geological and scientific study.


How Long Does Petrification Actually Take?

Petrification often conjures images of a painstakingly slow geological journey, typically spanning millions of years. However, this is not always the case — sometimes petrified wood forms much more quickly.

While it’s true that crafting the detailed and vibrantly hued specimens of petrified wood we often admire can stretch across long geological epochs, the inception of petrification can happen relatively quickly under the right conditions.


The speed of this process can vary significantly, depending on environmental factors. In some instances, it can happen relatively quickly, within decades or centuries, particularly when optimal conditions exist, such as the presence of abundant minerals and rapid burial.

Dazzling Chemistry

The level of detail seen in some fossilized specimens is downright astonishing. Petrified logs with well-preserved knots, branches and leaves have been found.

Fossil-hunters have also come across the occasional log with root structures attached to its base. In certain petrified log segments, it's possible to count the growth rings.


There's also the matter of coloration. Cross-sections of petrified wood often showcase a glistening rainbow of colors, which is why the fossils are so beloved by artists. The different hues are produced by different minerals. For example, some petrified logs have a red or pink tint. Internal hematite is responsible for this hue.

Now if there's a greenish color in your favorite hunk of wood, that means a mineral called "native iron" is inside the fossil. And shades of black are associated with "fool's gold" — also known as pyrite. Polishing petrified wood helps bring out the vibrance of these colors and patterns.


Is It Legal to Collect Petrified Wood Specimens?

The legality of collecting petrified wood varies based on the location and jurisdiction. In the United States, for example, collecting petrified wood is prohibited in national parks and monuments, such as the Petrified Forest National Park in Arizona, to preserve natural and cultural resources.

However, in certain areas managed by the Bureau of Land Management (BLM) or other public lands, limited collection of petrified wood for personal use might be allowed under specific regulations. Many countries and regions have their own sets of rules regarding fossil collection.


Legalities can also depend on factors like land ownership (private versus public), protected areas and intended use (personal versus commercial).

In many instances, ethical collecting also involves adhering to a "collecting code," which may entail only collecting where permitted, not using heavy equipment and avoiding disruption to wildlife and ecosystems. Engaging in responsible and legal collecting practices is crucial to preserving important paleontological resources for future generations and scientific study.

Always prioritize adherence to local laws and respect for the land and its resources when considering collecting petrified wood or any other geological specimens.


Finding Petrified Forests to Explore

While compiling a massive collection may be a legal nightmare, there's no law against marveling at the valuable fossil. You can find caches of petrified wood all over the world, from New Zealand to Greece to Argentina. Within the United States, there's an especially famous mother lode at the Petrified Forest National Park in eastern Arizona.

Over 200 million years ago, it was the site of a dense forest loaded with conifers and about a dozen other tree species. Log jams were often created when deceased trees fell into the prehistoric rivers that ran across the landscape. Scores of these plants were then buried rapidly in sediment and silica-rich volcanic ash.


Over in the Pacific Northwest, there's a much younger petrified forest with a more dramatic origin story. Around 15 million years ago, volcanic eruptions sent molten lava flowing across central Washington. Near the present-day city of Vantage, elms, sycamores, conifers and ginkgoes would periodically die and then sink to the bottom of local lakes.

Once that lava touched the lake water, it hardened into pillow basalt (an igneous rock formed by the cooling of molten magma or lava). This encased the logs, shielding them from oxygen and allowing the petrification process to occur.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.