Petrified Wood

Physical Properties

Hardness: 6.5–7 (Mohs). Color: Gray, tan, brown, or white. Luster: Vitreous to waxy. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.9.

Formation & Geological History

Formed through permineralization, a process where organic material is replaced by minerals (usually silica) while maintaining the original woody structure. It typically dates back millions of years (commonly Carboniferous to Cenozoic eras) in volcanic ash or sedimentary basins.

Uses & Applications

Used in high-end furniture (slabs), jewelry, lapidary arts for cabochons, and as ornamental display pieces in mineral collections.

Geological Facts

Famous locations like the Petrified Forest National Park in Arizona contain trees dating back over 200 million years. In some rare cases, opal or native copper replaces the wood instead of quartz.

Field Identification & Locations

Identify in the field by looking for distinct bark-like textures or growth rings on the exterior combined with a heavy, stone-like feel. It will scratch steel but not be scratched by it. Common in areas with historical volcanic activity and sedimentary deposits.

Identified on: 4/14/2026

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