sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, grey, black; Luster: Dull to vitreous/glassy; Crystal structure: Microcrystalline or amorphous (Quartz/Chalcedony); Cleavage: None; Specific Gravity: 2.6-2.9
- Hardness
- 6
- Color
- Brown, tan, grey, black
- Luster
- Dull to vitreous/glassy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, grey, black; Luster: Dull to vitreous/glassy; Crystal structure: Microcrystalline or amorphous (Quartz/Chalcedony); Cleavage: None; Specific Gravity: 2.6-2.9
Formation & geological history
Formed through permineralization when woody plant material is buried in sediment and organic matter is replaced by minerals, typically silicates, from groundwater over millions of years (often Triassic or Cenozoic).
Uses & applications
Used for decorative items, jewelry (cabochons), furniture (tabletops), and highly valued as geological collectibles.
Geological facts
The cell structure of the wood is often preserved in such detail that the original tree species can be identified microscopically; the 'Petrified Forest National Park' in Arizona is one of the most famous sites.
Field identification & locations
Identified by wood-like textures such as bark patterns or growth rings combined with a stony, heavy, and hard mineral feel. Common in areas with volcanic ash and ancient riverbeds.
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