fossil

Petrified Wood

Silicified Wood (primarily SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, gray, tan; Luster: Dull to waxy; Structure: Preserves original cellular plant structure; Cleavage: None/Conchoidal fracture; SG: 2.6-2.9

Hardness: 6
Color: Brown, gray, tan
Luster: Dull to waxy

Identified July 17, 2026More fossil →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, gray, tan; Luster: Dull to waxy; Structure: Preserves original cellular plant structure; Cleavage: None/Conchoidal fracture; SG: 2.6-2.9

Formation & geological history

Formed via permineralization where organic wood is replaced by silicon dioxide (quartz/chalcedony) over millions of years in anaerobic conditions, often under volcanic ash or river sediments. Estimated age: 20-300 million years.

Uses & applications

Used for lapidary work, jewelry (cabochons), interior decor, furniture (table slabs), and as a popular educational geological specimen.

Geological facts

The process preserves the wood structure so well that tree rings and cell walls can sometimes be seen under a microscope. It is the state gemstone of Washington and the state fossil of Arizona.

Field identification & locations

Identify by the bark-like exterior texture and internal ring patterns. Commonly found in areas with past volcanic activity or ancient river basins like the Petrified Forest National Park in Arizona.