sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Cream, tan, brown, or white; Luster: Dull to waxy; Crystal Structure: Microcrystalline (Cryptocrystalline) Quartz; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.9

Hardness: 6
Color: Cream, tan, brown, or white
Luster: Dull to waxy

Identified April 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization, a process where organic material is replaced by minerals (usually silica) while maintaining the original woody structure. This occurs when wood is buried under sediment or volcanic ash, excluding oxygen. Most specimens are Mesozoic to Cenozoic in age.

Uses & applications

Used primarily for decorative purposes, jewelry (cabochons), specimen collecting, lapidary art, and occasionally in furniture making like tabletops.

Geological facts

Petrified wood is the state gem of Washington and the state fossil of Arizona. In some cases, the replacement is so precise that cell structures are visible under a microscope.

Field identification & locations

Identify in the field by looking for woody textures, bark-like exteriors, or growth rings that feel heavy and hard like stone rather than light like wood. Common in the Petrified Forest National Park (Arizona) and various badlands ecosystems.