sedimentary
Petrified Wood
Silicified Wood (primarily SiO2 - Silicon Dioxide)
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, red, and gray; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None; Specific Gravity: 2.6-2.9
- Hardness
- 6
- Color
- Brown, tan, red, and gray
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, red, and gray; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None; Specific Gravity: 2.6-2.9
Formation & geological history
Formed via permineralization, where organic wood material is replaced by minerals (usually silica) from groundwater while buried under sediment or volcanic ash. Processes often date back to the Triassic (225 million years ago) or Neogene periods.
Uses & applications
Used primarily for decorative furniture (tabletops), lapidary work, jewelry, and as a popular geological collecting specimen.
Geological facts
Petrified wood is the state fossil of Arizona. The process happens in an anaerobic environment which prevents rot, allowing minerals to replicate the tree's cellular structure in stone.
Field identification & locations
Identify in the field by looking for bark-like textures on the exterior and visible growth rings on cross-sections. Commonly found in the American Southwest (Petrified Forest National Park), Madagascar, and Indonesia.
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