sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, black, and white; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (Chalcedony/Quartz replacement); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9

Hardness: 6
Color: Brown, tan, black, and white
Luster: Vitreous to waxy

Identified June 6, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

Formed when plant material is buried by sediment or volcanic ash and protected from decay by oxygen and organisms. Liquid rich in silica (groundwater) flows through the sediment, replacing the plant material cell by cell with minerals. Most specimens are from the Mesozoic or Cenozoic eras.

Uses & applications

Commonly used in jewelry (cabochons), interior design (tables, bookends), and as high-value lapidary and collector specimens.

Geological facts

Unlike most fossils, which are impressions, petrified wood is a 3D mineral replacement that can preserve the original internal cellular structure of the tree. The colors are caused by trace elements: iron (reds/yellows), manganese (pinks/purples), or carbon (blacks).

Field identification & locations

Identify by looking for preserved wood grain, bark textures, or growth rings in a rock that is heavy and cannot be scratched by a steel knife. Common in the Western US (Arizona, Oregon), Madagascar, and Indonesia.