metamorphic
Petrified Wood
Silicified wood (Quartz, SiO2)
Hardness: 6.5-7 on the Mohs scale. Color: brown, tan, cream, and black with visible grain patterns. Luster: dull to vitreous (glassy). Crystal structure: Trigonal/Amorphous (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.9.
- Hardness
- 6
- Color
- brown, tan, cream, and black with visible grain patterns
- Luster
- dull to vitreous (glassy)
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Physical properties
Hardness: 6.5-7 on the Mohs scale. Color: brown, tan, cream, and black with visible grain patterns. Luster: dull to vitreous (glassy). Crystal structure: Trigonal/Amorphous (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.9.
Formation & geological history
Formed through permineralization, where organic wood is buried under sediment or volcanic ash, and water rich in silica minerals flows through it, replacing the wood cells with minerals over millions of years (commonly Carboniferous to Cenozoic eras).
Uses & applications
Used primarily for lapidary work, jewelry (cabochons), interior decoration, furniture (tabletops), and as highly sought-after display specimens for mineral collectors.
Geological facts
In many specimens, the cellular structure of the wood is so perfectly preserved that the specific tree species can be identified. Famous deposits include the Petrified Forest National Park in Arizona, which contains logs that are over 225 million years old.
Field identification & locations
Identify in the field by looking for distinct bark-like textures, tree rings, and wood grain on a stony, heavy material that cannot be scratched by a steel knife. Common in sedimentary basins and areas with historical volcanic activity like Arizona, Oregon, and Madagascar.
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