sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5–7 (Mohs scale), Color: Dark brown to black with tan streaks, Luster: Waxy to dull, Structure: Cryptocrystalline quartz substituting organic matter, Cleavage: None

Hardness: 6

Identified June 4, 2026More sedimentary →

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Physical properties

Hardness: 6.5–7 (Mohs scale), Color: Dark brown to black with tan streaks, Luster: Waxy to dull, Structure: Cryptocrystalline quartz substituting organic matter, Cleavage: None

Formation & geological history

Formed when trees are buried by sediment and volcanic ash, and through permineralization, silica replaces the wood fibers over millions of years (commonly Triassic to Cenozoic periods).

Uses & applications

Used for decorative items, jewelry (cabochons), furniture tops, and as a popular geological collectible.

Geological facts

The process happens in low-oxygen environments to prevent decay. Arizona's Petrified Forest National Park contains one of the world's most famous deposits dating back 225 million years.

Field identification & locations

Identify in the field by looking for bark textures, growth rings, and wood grain preserved in stone. Found in ancient floodplains or volcanic ash beds.