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"Petrified wood" (from the Greek word PETRO for "rock" or "stone") literally means "wood turned into stone". It's the name given to a special type of fossilized remains of tree or tree-like plants having completely transitioned to stone by the process in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue.

All the organic materials have been replaced with minerals (mostly a silicate, such as quartz), while retaining the original structure of the stem tissue in all its detail, down to the microscopic level. Structures such as tree rings and the various tissues are often observed features. The petrifaction process occurs underground, when wood becomes buried under sediment and is initially preserved due to a lack of oxygen. In general, stem tissue takes less than one thousand years to petrify.

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Different elements in the water/mud during the petrification process give petrified wood a variety of color ranges: carbon - black, cobalt - green/blue, chromium - green/blue, copper - green/blue, iron oxides - red, brown, and yellow, manganese - pink/orange, manganese oxides - blackish/yellow.

Petrified wood sites in the USA include: Petrified Wood Park in Lemmon (South Dakota), Petrified Forest National Park (Arizona), Petrified Forest (California), Mississippi Petrified Forest in Flora (Mississippi), Florissant Fossil Beds National Monument near Florissant (Colorado), Yellowstone National Park (Wyoming), The south unit of Theodore Roosevelt National Park outside Medora (North Dakota), Gilboa Fossil Forest (New York), Escalante Petrified Forest State Park (Utah), Petrified Springs in Kenosha (Wisconsin).

Artificial petrified wood has been produced in a Washington laboratory. In the process small cubes of pine are soaked in an acid bath for two days, then in a silica solution for another two. The product is then cooked at 1400 grades of Centigrade in an argon atmosphere for two hours. The result was silicon carbide ceramic which preserved the intricate cell structure of the wood.