sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Brown, tan, ocher, and gray. Luster: Vitreous to waxy. Crystal structure: Cryptocrystalline (Microcrystalline Quartz). Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.9.

Hardness: 6
Color: Brown, tan, ocher, and gray
Luster: Vitreous to waxy

Identified June 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization when woody plant material is buried in sediment and saturated with mineral-rich water, typically volcanic ash or groundwater. Over millions of years (often Mesozoic or Cenozoic), silica replaces the organic tissue. This specimen shows distinct horizontal wood grain or cell structure preserved in stone.

Uses & applications

Used primarily for lapidary work, jewelry (cabochons), interior decor (tabletops, bookends), and as an educational geological specimen.

Geological facts

Famous locations include the Petrified Forest National Park in Arizona. Petrified wood is both a fossil and a rock, where the original cellular structure of the tree is often preserved in cellular detail despite being entirely mineralized.

Field identification & locations

Identify by looking for preserved growth rings, bark texture, or fibrous wood grain patterns on a heavy, hard rock. It cannot be scratched by a steel knife. Common in sedimentary basins and areas with historical volcanic activity.