metamorphic
Petrified Wood
Silicified Wood (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Tan, brown, reddish-brown, and grey; Luster: Dull to waxy/vitreous; Structure: Cryptocrystalline (replacing organic wood fiber); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.9
- Hardness
- 6
- Color
- Tan, brown, reddish-brown, and grey
- Luster
- Dull to waxy/vitreous
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Tan, brown, reddish-brown, and grey; Luster: Dull to waxy/vitreous; Structure: Cryptocrystalline (replacing organic wood fiber); 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 structure of the wood. This typically occurs when wood is buried under sediment or volcanic ash. Geological age can range from the Devonian (390 million years ago) to the Pleistocene.
Uses & applications
Used in lapidary arts for jewelry, bookends, and decorative sculptures. Larger specimens are used in landscape design and high-end furniture (e.g., tabletops). It is a popular item for geological and fossil collectors.
Geological facts
Petrified wood is the state stone of Washington and the state fossil of Arizona. The Petrified Forest National Park in Arizona contains one of the world's largest concentrations of petrified wood, mostly from the Triassic period roughly 225 million years ago.
Field identification & locations
Identify in the field by the presence of wood-like grain, bark textures, and growth rings in a heavy, stone-like material. It is commonly found in sedimentary basins, particularly in the Western United States (Arizona, Oregon, Washington). Collectors should look for distinct cellular preservation and color variety.
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