sedimentary
Petrified Wood
Silicified wood (Quartz / Chalcedonized wood, SiO2)
Hardness: 6.5 to 7 on the Mohs scale; Color: Tan, gray, white, and brown with fibrous wood-grain textures; Luster: Vitreous to waxy; Crystal structure: Microcrystalline quartz (chalcedonized); Cleavage: None (conchoidal fracture); Specific gravity: 2.5 to 2.7.
- Hardness
- 6
- Color
- Tan, gray, white, and brown with fibrous wood-grain textures
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5 to 7 on the Mohs scale; Color: Tan, gray, white, and brown with fibrous wood-grain textures; Luster: Vitreous to waxy; Crystal structure: Microcrystalline quartz (chalcedonized); Cleavage: None (conchoidal fracture); Specific gravity: 2.5 to 2.7.
Formation & geological history
Formed through permineralization, where organic wood materials are completely replaced by minerals (usually quartz, opal, or chalcedon) over millions of years when buried in oxygen-depleted sediment under mineral-rich groundwater. Geological age ranges from Triassic to Eocene, roughly 50 to 225 million years old.
Uses & applications
Used for lapidary work, decorative ornamental objects, bookends, high-end jewelry, and as collectible museum or display specimens.
Geological facts
Petrified wood retains the exact microscopic structure of the original tree, allowing scientists to identify ancient plant species millions of years after extinction. Famous locations include the Petrified Forest National Park in Arizona.
Field identification & locations
Easily identified by its wood-like grain and exterior texture combined with the extreme hardness, weight, and cold touch of stone. Found worldwide in sedimentary rock layers associated with ancient river floodplains and volcanic ash beds.
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