sedimentary

Petrified Wood

Silicified Wood (primarily SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, reddish-brown, grey; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (chalcedony/quartz replacement); Cleavage: None; Specific gravity: 2.6-2.9.

Hardness: 6
Color: Brown, tan, reddish-brown, grey
Luster: Vitreous to waxy

Identified June 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via permineralization where organic plant material is replaced by silica (quartz) from groundwater while buried under sediment or volcanic ash. This typically occurs over millions of years, often dating back to the Triassic or Teocene periods.

Uses & applications

Used for lapidary work such as jewelry (cabochons), bookends, decorative table tops, and as a popular educational and ornamental collector specimen.

Geological facts

The cell structure of the original tree is often preserved in such detail that the species of the tree can be identified under a microscope. Arizona's Petrified Forest National Park contains one of the world's largest concentrations of these fossils.

Field identification & locations

Identify in the field by looking for wood-like texture, bark patterns, or growth rings preserved in a stony, heavy material that cannot be scratched by a steel knife. Common in areas with ancient volcanic activity and sedimentary basins.