sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 7 (Mohs scale), Color: combinations of grey, brown, red, and orange, Luster: Vitreous to waxy, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.9

Identified June 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via permineralization where organic wood materials are replaced by silica (usually chalcedony or quartz) by mineral-rich groundwater over millions of years, often in volcanic ash beds or fluvial sediments during the Triassic to Tertiary periods.

Uses & applications

Used for lapidary work, jewelry (cabochons), ornamental furniture (bookends, tabletops), and as a popular collector's specimen.

Geological facts

Arizona's Petrified Forest National Park contains one of the world's largest concentrations of petrified wood from the Late Triassic. If the wood was replaced by opal rather than quartz, it is known as opalized wood.

Field identification & locations

Identify in the field by looking for bark-like textures on the exterior and a smooth, stony, or glass-like interior. Commonly found in Arizona, Oregon, and Washington in the US, as well as Madagascar and Brazil.