sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
Hardness: 6.5-7 on Mohs scale; Color: typically browns, grays, and tans (can show reds/blues depending on trace minerals); Luster: vitreous to waxy; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None
- Hardness
- 6
- Luster
- vitreous to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: typically browns, grays, and tans (can show reds/blues depending on trace minerals); Luster: vitreous to waxy; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None
Formation & geological history
Formed via permineralization where organic wood materials are replaced by minerals (usually silica) in an anaerobic environment. This process typically occurs over millions of years, often in volcanic ash beds or river sediments; ages range from the Devonian to the Pleistocene.
Uses & applications
Used in decorative art, high-end furniture (slabs), jewelry (cabochons), and as a popular specimen for geological and fossil collecting.
Geological facts
Despite being made of stone, the specimen often retains the original cellular structure of the wood, including bark patterns and growth rings. Arizona's Petrified Forest National Park contains one of the world's largest concentrations of this material.
Field identification & locations
Identify in the field by looking for a 'woody' texture or bark-like exterior on a heavy, dense rock that cannot be scratched by a steel knife. Common in areas with ancient volcanic activity and sedimentary basins like the American Southwest and Madagascar.
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