metamorphic
Petrified Wood
Silicified wood (Quartz, SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, cream, and grey with wood-grain patterns; Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None; Specific Gravity: 2.5-2.8.
- Hardness
- 6
- Color
- Brown, tan, cream, and grey with wood-grain patterns
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, cream, and grey with wood-grain patterns; Luster: Vitreous to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None; Specific Gravity: 2.5-2.8.
Formation & geological history
Formed through permineralization when woody debris is buried under sediment and volcanic ash, then submerged in mineral-rich water. Over millions of years (often Triassic or Cenozoic), silica replaces the organic material molecule by molecule.
Uses & applications
Used primarily in jewelry (cabochons), lapidary art, furniture décor (tabletops), and as highly collectible fossil specimens for education and display.
Geological facts
Petrified wood is the state gem of Washington and the state fossil of Arizona. The Petrified Forest National Park in Arizona contains one of the world's largest concentrations of these fossils, some dating back 225 million years.
Field identification & locations
Identify by looking for preserved growth rings, bark textures, or knots within a stone that feels heavy and cold like quartz. Common in riverbeds and arid badlands; collectors should look for smooth, water-worn pieces or rough chunks showing cellular detail.
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