sedimentary

Petrified Wood

Silicified Wood (primarily SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Brown, tan, grey; Luster: Vitreous to dull; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.9

Hardness: 6
Color: Brown, tan, grey
Luster: Vitreous to dull

Identified June 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization where organic wood materials are replaced by minerals (usually silica) over millions of years in anaerobic conditions, often under volcanic ash or river sediments. Most specimens range from 20 to 300 million years old.

Uses & applications

Used for decorative items, jewelry (cabochons), furniture (tabletops), and as highly collectible geological specimens.

Geological facts

This is a fossil where the original cellulose and lignin have been replaced by silica while often retaining the original microscopic structure of the tree bark and rings. Arizona's Petrified Forest National Park contains one of the world's largest concentrations of it.

Field identification & locations

Identify by looking for wood-like grain, bark textures, or growth rings in a heavy, stone-hard material. Common in areas with ancient volcanic activity and sedimentary basins. Collectors should look for 'agatized' sections which show colorful translucency.