metamorphic
Petrified Wood (Agatized/Silicified Wood)
Silicified Wood (SiO2 - Silicon Dioxide)
Hardness: 6.5–7 on Mohs scale. Color: Highly variable (tans, browns, yellows, and white in this specimen). Luster: Vitreous to waxy. Structure: Cryptocrystalline quartz (chalcedony/agate) replacing original cellulose. Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Highly variable (tans, browns, yellows, and white in this specimen). Luster: Vitreous to waxy. Structure: Cryptocrystalline quartz (chalcedony/agate) replacing original cellulose. Cleavage: None (conchoidal fracture).
Formation & geological history
Formed when plant material is buried by sediment and protected from decay by oxygen and organisms. Over millions of years (typically Triassic to Cenozoic), groundwater rich in dissolved silica flows through the sediment, replacing the plant cell walls with minerals.
Uses & applications
Used primarily for ornamental purposes, lapidary art, jewelry (cabochons), furniture (slices for tabletops), and as a popular geological collectible.
Geological facts
In some specimens, the replacement is so perfect that cell structures and growth rings are visible under a microscope. Arizona's Petrified Forest National Park contains one of the world's largest concentrations of these fossils.
Field identification & locations
Identify in the field by looking for a 'bark' texture on the exterior or concentric ring patterns similar to modern wood. It is much heavier and harder than real wood and will not scratch with a steel knife. Common in volcanic ash regions or old riverbeds.
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