sedimentary

Petrified Wood

Silicified Wood (primarily SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, gray, tan with visible wood grain; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Brown, gray, tan with visible wood grain
Luster: Vitreous to waxy

Identified June 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when organic plant material is buried by sediment and replaced by silica (permineralization) over millions of years, often in volcanic ash environments. Dates from various periods, often Carboniferous to Cenozoic.

Uses & applications

Used for jewelry (cabochons), interior decoration (tables, bookends), landscaping, and as a popular educational/collector specimen.

Geological facts

Petrified wood is a fossil in which all digestive matter has been replaced with minerals, while retaining the original structure of the stem tissue. Arizona's Petrified Forest National Park is one of the most famous locations for it.

Field identification & locations

Identify by looking for growth rings, wood grain textures, and bark-like outer surfaces. Often found in riverbeds or areas with historic sedimentary deposits. Collectors look for high color contrast and preservation of cellular detail.