sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5–7 (Mohs scale); Color: Gray, brown, or tan with wood grain patterns; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline quartz/chalcedony); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.9

Hardness: 6
Color: Gray, brown, or tan with wood grain patterns
Luster: Vitreous to dull

Identified June 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization when plant material is buried by sediment and volcanic ash, then replaced by minerals flows through groundwater, typically occurring over millions of years (often from the Triassic, Jurassic, or Cenozoic eras).

Uses & applications

Used primarily for lapidary work, jewelry, interior decoration (tabletops, bookends), and as educational fossils in museum collections.

Geological facts

Petrified wood is the state stone of Washington and the state fossil of Arizona. The organic matter is completely replaced by silica, but the original cellular structure of the tree is often preserved.

Field identification & locations

Identify by looking for bark textures, growth rings, or wood-like striations on an extremely hard, stone surface. Commonly found in areas with past volcanic activity and river basins like the Petrified Forest National Park in Arizona.