What Is Petrified Wood?

Rockhounding is all about the thrill of the hunt. And lucky for rock enthusiasts in Utah, the Beehive State owns spectacular formations of petrified wood. Petrified (or fossilized) wood occurs when minerals like quartz or agate invade the cavities of natural wood over many years. Unlike impressions of plant fossils, petrified wood is a three-dimensional representation of original, organic material. 

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How Does Wood Petrify?

Wood petrification happens underground when water-saturated sediment or volcanic ash buries the wood. The water reduces oxygen levels, which slows decomposition by bacteria or fungi. Mineral-filled water flows through deposits, where minerals over millions of years slowly replace the plant’s cell walls.

For wood to petrify, the following factors must be in place:

  • Absence of oxygen: The lack of oxygen slows wood’s decay, which allows minerals to replace cell walls and fill void spaces in the wood. 
  • Presence of silica-rich liquids: Silica is a naturally existing compound in organic and inorganic materials. Glass, beach sand, granite and silicone are all silica materials. When wood soaks up silica-rich fluids, it crystalizes as solid minerals. 
  • High pressure over time: When ash, mud or sand buries wood for centuries, the high-pressure environment allows inorganic compounds to replace organic plant material.

What Is It Made From?

The minerals that typically fill in cavities to create petrified wood include quartz, chalcedony, agate and opal. 

  • Quartz: Hard, crystalline mineral made of silica. 
  • Chalcedony: Cryptocrystalline form of silica composed of extremely fine intergrowth of quartz and moganite. 
  • Agate: Translucent, microcrystalline variety of quartz. 
  • Opal: Hydrated amorphous form of silica.

Petrified wood seen at Escalante Petrified Forest State Park.

Photo: Utah State Parks

Petrified wood does not have a strict classification system. It is typically identified based on color and mineral composition.

Photo: Utah State Parks

Depending on their oxidation state, trace metals, particularly iron, can produce a range of hues in petrified wood.

Photo: Utah State Parks

Identifying Petrified Wood

Types Of Petrified Wood

Petrified wood does not have a strict classification system. It is typically identified based on color and mineral composition.

Homogeneous Type: The homogeneous type of petrified wood is the most common. It shows a uniformed ring color and is generally light-colored and composed primarily of opal. 

Spotted Petrified Wood: A more decorative type of wood because of the unique spots, this wood combines opal and chalcedony. 

Jet-Like Petrified Wood: Petrified wood displays clear lines that sometimes form wavy patterns. 

Concentric Texture: Wood with various color layers saturated by different minerals create different colors. It’s composed of layers of opal and chalcedony that change over time to develop the concentric texture. 

Lens-Shaped or Peanut Texture: A peanut or lens-shaped structure forms when minerals fill existing wood cavities. This can sometimes result in a black-and-white wood pattern. 

Colors of Petrified Wood

So, how does petrified wood get all its beautiful, unique coloring? Trace metals! More specifically, iron, chromium, manganese, copper and cobalt. These metals, particularly iron, can produce a range of hues depending on their oxidation state. Color variations usually reflect different stages of mineralization:

Black: The wood contains carbon. 

Blue, Teal and Green: The wood contains copper, cobalt or chromium.

Orange and Yellow: The wood contains manganese oxides.

Pink and Purple: The wood contains manganese. 

Brown: The wood contains iron oxides.

petrified-wood-escalante-state-park-matt-morgan

Escalante Petrified Forest State Park

Escalante, UT

The Escalante Petrified Forest State Park is located at Wide Hollow Reservoir. This small reservoir is popular for boating, canoeing, and fishing.

Escalante Petrified Forest State Park

Collecting Petrified Wood

Can You Collect Petrified Wood?

Rockhounding restrictions vary based on land designations. Federal lands, such as BLM and U.S. Forest Lands, generally permit recreational rockhounding in reasonable quantities. 

Collecting is not allowed under any circumstances in national parks, monuments, tribal lands, military reservations, dam sites or wildlife refuges. Collecting for commercial purposes is never allowed without a permit. 

According to the BLM Rock, Mineral and Fossil Collecting guidelines: “Petrified wood may be collected for personal use up to 25 pounds plus one piece per day up to 250 pounds per calendar year. The use of explosives and/or power equipment is forbidden. Collectors wishing to resell their petrified wood specimens must obtain a permit.”

Collecting guidelines for petrified wood

Found Something You Can't Identify?

Rockhounding is all about the thrill of discovery. If you’ve found something you can’t identify, check for information online from geology.utah.gov. A local gem store may have some insights if this doesn't yield answers. Still no luck? Schedule an appointment with your local museum or university to help identify your specimen. 

If you discover an artifact, do NOT touch or remove it. Take a photo, note the location and contact your local BLM office. 

Report an Artifact

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