fossil

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 Mohs; Color: Brown, gray, reddish-tan; Luster: Waxy to vitreous (dull if unpolished); Crystal Structure: Cryptocrystalline (chalcedony/quartz replaces organic cells); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.9

Hardness: 6
Color: Brown, gray, reddish-tan
Luster: Waxy to vitreous (dull if unpolished)

Identified July 15, 2026More fossil →

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Physical properties

Formation & geological history

Formed through permineralization, a process where organic wood is buried by sediment or volcanic ash. Groundwater rich in dissolved silica flows through the sediment, replacing the plant material with minerals over millions of years (typically Carboniferous to Pleistocene ages).

Uses & applications

Used for ornamental carvings, jewelry (cabochons), furniture (slices for tables), and as a highly collectible specimen for paleontologists and hobbyists.

Geological facts

Petrified wood can sometimes preserve the cellular structure of the original tree so well that the species can be identified under a microscope. Arizona's Petrified Forest National Park contains one of the largest concentrations in the world.

Field identification & locations

Identify by looking for bark textures, growth rings, and wood grain patterns preserved in stone. It feels significantly heavier than natural wood and cannot be scratched by a steel knife. Common in areas with ancient volcanic activity and sedimentary basins.