sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness of 7 on the Mohs scale, colors range from brown, tan, yellow, to red and black depending on mineral impurities, waxy to vitreous luster, amorphous to microcrystalline quartz structure, conchoidal fracture with no true cleavage, specific gravity around 2.65.

Identified July 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when organic plant material is buried in an oxygen-deficient environment under sediment, preventing decay. Groundwater rich in dissolved silica flows through the sediment, replacing the original wood cell walls with microcrystalline quartz, opal, or chalcedony over millions of years.

Uses & applications

Used for making decorative items, jewelry, bookends, table tops, carvings, and as sought-after specimens for rock and mineral collectors.

Geological facts

Petrified wood retains the original cellular structure of the tree, allowing scientists to study ancient plant life and prehistoric ecosystems dating back hundreds of millions of years.

Field identification & locations

Can be identified in the field by its distinct wood-like grain and bark texture combined with a stone-like weight and hardness that easily scratches glass. Common locations include the Petrified Forest in Arizona, USA, and various sites worldwide.