metamorphic
Petrified Wood
Silicified wood (primarily Silicon Dioxide, SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, yellow, and reddish hues; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9
- Hardness
- 6
- Color
- Brown, tan, yellow, and reddish hues
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, yellow, and reddish hues; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9
Formation & geological history
Formed through permineralization where organic wood material is replaced by silica minerals, typically quartz, over millions of years (often Triassic to Eocene). Occurs when trees are buried by sediment or volcanic ash, excluding oxygen.
Uses & applications
Used for ornamental carvings, jewelry (cabochons), furniture (tabletops), and as highly prized geological display specimens.
Geological facts
Famous specimens are found in the Petrified Forest National Park in Arizona. The variation in colors is caused by trace elements: iron produces reds/browns, manganese produces purples, and copper/chrome produce greens.
Field identification & locations
Identify in the field by looking for bark-like textures or tree rings on a rock that is heavy and hard enough to scratch glass. Common in badlands and areas with ancient volcanic activity.
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