sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Variegated brown, red, grey, and tan; Luster: Vitreous to waxy; Structure: Cryptocrystalline quartz preserving cellular organic structure; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.9

Hardness: 6
Color: Variegated brown, red, grey, and tan
Luster: Vitreous to waxy

Identified June 21, 2026More sedimentary →

Explore Petrified Wood in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through permineralization where organic material is replaced by minerals, typically silica, under anaerobic conditions in sedimentary basins. Most common in Triassic and Jurassic deposits (~200 million years old) where volcanic ash provided silica.

Uses & applications

Used for decorative items, clock faces, bookends, jewelry (cabochons), and high-end table tops. It is also a popular specimen for geological collectors.

Geological facts

Unlike typical fossils which are impressions, petrified wood is a three-dimensional replacement of the original plant matter. The colors are caused by trace elements: iron produces reds/browns, manganese produces purples, and copper creates greens.

Field identification & locations

Identify in the field by looking for distinct bark-like textures or growth rings on an object that feels like stone and cannot be scratched by a steel knife. Common in Arizona (Petrified Forest National Park), Madagascar, and Indonesia.