sedimentary
Petrified Wood
Silicified wood (Quartz/Chalcedony - SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and reddish-grey. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.9.
- Hardness
- 6
- Color
- Brown, tan, and reddish-grey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and reddish-grey. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.9.
Formation & geological history
Forms when wood is buried under sediment or volcanic ash, and water rich in dissolved silica flows through, replacing the organic matter with mineral. Often originates from the Triassic, Jurassic, or Cretaceous periods.
Uses & applications
Used primarily for lapidary work, jewelry (cabochons), interior decoration, and as popular educational fossils and collector specimens.
Geological facts
The most famous location for this is the Petrified Forest National Park in Arizona. It is the state fossil of Washington and the state rock of Mississippi.
Field identification & locations
Look for visible wood grain, bark textures, or cellular structures preserved in stone. It feels significantly heavier and colder than real wood. Commonly found near ancient river beds or volcanic ash deposits.
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