Petrified Wood

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Brown, grey, black, tan with grain texture. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.9.

Formation & Geological History

Formed when plant material is buried by sediment and protected from decay by oxygen and organisms. Groundwater rich in dissolved solids flows through the sediment, replacing original plant material with silica, calcite, or pyrite. Often associated with the Triassic to Eocene periods.

Uses & Applications

Used in jewelry (cabochons), interior design (furniture, bookends), and highly valued by fossil and mineral collectors.

Geological Facts

Petrified wood is the state gem of Washington and the state fossil of Arizona. The famous Petrified Forest National Park in Arizona contains trees that are over 225 million years old.

Field Identification & Locations

Identify in the field by characteristic wood grain, bark textures, or growth rings preserved in stone. It feels significantly heavier and colder than real wood and cannot be scratched by a steel knife.

Identified on: 4/14/2026

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