sedimentary

Petrified Wood

Silicified Wood (primarily SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Gray, black, white, brown. Luster: Vitreous to dull. Crystal structure: Cryptocrystalline (chalcedony/quartz). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.9.

Hardness: 6
Color: Gray, black, white, brown
Luster: Vitreous to dull

Identified June 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via permineralization where organic plant material is replaced by minerals, typically silica, in anaerobic conditions such as burial under volcanic ash or river sediments. Most specimens range from Devonian to Pleistocene in age.

Uses & applications

Used for jewelry (cabochons), lapidary art, decorative bookends, furniture segments, and as a popular teaching and collecting specimen.

Geological facts

Petrified wood is the state fossil of several US states including Arizona. In some cases, the replacement is so perfect that the internal cellular structure of the original tree is visible under a microscope.

Field identification & locations

Identify in the field by looking for bark textures, growth rings, and wood-like grain patterns in a material that is as hard as stone. Found globally in 'fossil forests' like those in Arizona, USA, or Madagascar.