metamorphic
Petrified Wood
Silicified wood (primarily Silicon Dioxide, SiO2)
Hardness: 6.5–7 on Mohs scale. Color: Tans, browns, and grays. Luster: Vitreous to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.9.
- Hardness
- 6
- Color
- Tans, browns, and grays
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale. Color: Tans, browns, and grays. Luster: Vitreous to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6–2.9.
Formation & geological history
Formed through permineralization where organic plant matter is replaced by minerals, typically silica, over millions of years. This specimen displays wood grain textures from the original tree or log.
Uses & applications
Used for ornamental carvings, jewelry (cabochons), furniture tops, and as a popular collectable for geological study.
Geological facts
Petrified wood is the state stone of Washington and the state fossil of Arizona. The organic cell structure can sometimes be so perfectly preserved that it can be studied under a microscope to determine the tree species.
Field identification & locations
Look for wood-like textures such as bark patterns, knots, or growth rings. Found globally in ancient riverbeds or volcanic ash deposits; famous locations include the Petrified Forest National Park in Arizona.
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