metamorphic
Petrified Wood
Silicified Wood (SiO2 - Silicon Dioxide)
Hardness: 6.5–7 on Mohs scale; Color: Tan, brown, white, and black (due to iron or manganese oxides); Luster: Sub-vitreous to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7
- Hardness
- 6
- Luster
- Sub-vitreous to waxy
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Tan, brown, white, and black (due to iron or manganese oxides); Luster: Sub-vitreous to waxy; Structure: Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7
Formation & geological history
Formed through permineralization where organic wood is replaced by silica minerals (usually chalcedony or opal) in low-oxygen environments like volcanic ash or river delta sediments. Most common specimens are from the Triassic, Jurassic, or Cenozoic periods.
Uses & applications
Used primarily for decorative purposes, lapidary art, jewelry, furniture (such as table tops), and as scientific specimens for studying paleo-botany.
Geological facts
Petrified wood is the state stone of Washington and the state fossil of Arizona. The process is so precise that cell structures and tree rings are often preserved in stone for millions of years.
Field identification & locations
Identify in the field by looking for distinct wood grain patterns, bark-like external textures, and growth rings on cross-sections. Commonly found in Arizona (Petrified Forest NP), Oregon, and Madagascar. Collectors should look for pieces with high polish and vibrant color contrast.
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