sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Tan, brown, white (variable due to impurities like iron or manganese); Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (usually chalcedony or quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.9.

Hardness: 6
Luster: Vitreous to waxy

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via permineralization where organic wood materials are replaced with minerals, typically silica, under anaerobic conditions. Most specimens range from the Devonian period (390 million years ago) to the more common specimens from the Triassic, Jurassic, or Cenozoic eras.

Uses & applications

Used in ornamental jewelry (cabochons), interior design (polished tabletops/bookends), and as teaching specimens in paleontology and geology.

Geological facts

Petrified wood is the state gem of Washington and the state fossil of Arizona. The Petrified Forest National Park in Arizona is one of the most famous locations, featuring massive logs that are over 200 million years old.

Field identification & locations

Identify in the field by looking for distinct wood grain patterns, growth rings, or bark textures preserved in stone. It is commonly found in areas of ancient volcanic activity or sedimentary basins. Note that it will be much heavier and harder than actual wood and will not burn.