sedimentary
Petrified Wood
Silicified Wood (primarily Quartz / Chalcedony: SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Reddish-brown, tan, and grey; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.6–2.9.
- Hardness
- 6
- Color
- Reddish-brown, tan, and grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Reddish-brown, tan, and grey; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.6–2.9.
Formation & geological history
Formed when organic plant material is buried by sediment or volcanic ash, protecting it from oxygen. Groundwater rich in dissolved minerals (usually silica) flows through the sediment, replacing the organic plant cells with minerals over millions of years. Most common during the Mesozoic Era.
Uses & applications
Used for ornamental carvings, jewelry (cabochons), lapidary work, high-end furniture (slabs), and as a popular geological collectible.
Geological facts
Petrified wood can preserve the cellular structure of original trees so accurately that the species can often be identified. The Painted Desert in Arizona contains one of the world's most famous concentrations of petrified logs.
Field identification & locations
Identify by looking for bark-like textures or growth rings on the exterior combined with a heavy, stone-like feel and extreme hardness (it will scratch glass). Commonly found in sedimentary basins and area of past volcanic activity.
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