sedimentary

Petrified Wood

Silicified wood (Quartz/Chalcedony - SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and reddish-grey. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.9.

Hardness: 6
Color: Brown, tan, and reddish-grey
Luster: Waxy to vitreous

Identified May 26, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and reddish-grey. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.9.

Formation & geological history

Forms when wood is buried under sediment or volcanic ash, and water rich in dissolved silica flows through, replacing the organic matter with mineral. Often originates from the Triassic, Jurassic, or Cretaceous periods.

Uses & applications

Used primarily for lapidary work, jewelry (cabochons), interior decoration, and as popular educational fossils and collector specimens.

Geological facts

The most famous location for this is the Petrified Forest National Park in Arizona. It is the state fossil of Washington and the state rock of Mississippi.

Field identification & locations

Look for visible wood grain, bark textures, or cellular structures preserved in stone. It feels significantly heavier and colder than real wood. Commonly found near ancient river beds or volcanic ash deposits.