sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Brown, red, grey, and pink hues, Luster: Vitreous to waxy, Crystal Structure: Cryptocrystalline quartz (Chalcedony/Agate), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.9

Hardness: 6

Identified June 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via permineralization where organic wood materials are replaced by minerals (primarily silica) over millions of years, often starting in the Triassic period (~225 million years ago) when trees were buried under volcanic ash or sediment.

Uses & applications

Used for decorative objects like bookends, tabletops, and jewelry (cabochons). Highly valued by fossil collectors and for educational purposes in museums.

Geological facts

The Petrified Forest National Park in Arizona is one of the most famous sites for these fossils. It is the state fossil of Arizona and Washington. Despite looking like wood, it is entirely stone and contains no original organic matter.

Field identification & locations

Identify by looking for preserved wood grain, bark textures, or tree rings in a heavy, stony material. Commonly found in sedimentary basins and areas with historical volcanic activity. Collectors should look for vibrant colors and intact cell structures.