metamorphic
Petrified Wood
Silicified Wood (primarily SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Shades of brown, tan, and dark grey due to iron and manganese oxides; Luster: Vitreous to dull; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.9.
- Hardness
- 6
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Shades of brown, tan, and dark grey due to iron and manganese oxides; Luster: Vitreous to dull; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.9.
Formation & geological history
Formed through permineralization over millions of years (often from the Triassic, Jurassic, or Cenozoic eras). This occurs when organic plant material is buried by sediment or volcanic ash, and mineral-rich groundwater replaces the wood cells with silica, preserving the original structure.
Uses & applications
Used in lapidary work for jewelry, bookends, tabletops, and as decorative display specimens for collectors.
Geological facts
Petrified wood is the state gemstone of Washington and the state fossil of Arizona. The famous Petrified Forest National Park in Arizona contains specimens that are over 225 million years old.
Field identification & locations
Identify in the field by looking for distinct wood grain patterns, bark textures, or growth rings in a heavy, stony material. It is commonly found in areas with history of volcanic activity and sedimentary basins, such as the Western United States, Madagascar, and Indonesia.
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