sedimentary
Petrified Wood
Silicified Wood (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-brown with cream streaks; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9
- Hardness
- 6
- Color
- Brown, tan, reddish-brown with cream streaks
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-brown with cream streaks; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9
Formation & geological history
Formed via permineralization where organic wood materials are replaced by silica (quartz or chalcedony) while buried in sediment or volcanic ash. This typically occurs over millions of years, often dating to the Triassic or Cenozoic eras.
Uses & applications
Used in lapidary work for jewelry, bookends, furniture tops, and popular among rock collectors for display.
Geological facts
The organic structure of the wood, including rings and bark, is often perfectly preserved in stone. The colors are caused by trace elements like iron (red/orange) or manganese (black).
Field identification & locations
Identified by the distinct look of tree bark or wood grain in a heavy, cold stony material. Commonly found in Arizona (USA), Madagascar, and Indonesia. Look for wood-like texture that cannot be scratched by a steel knife.
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