metamorphic
Petrified Wood (Silicified Wood)
Silicified fossil wood (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, grey, and black banding. Luster: Vitreous to dull. Crystal structure: Cryptocrystalline (chalcedony/quartz). Specific gravity: 2.6-2.9.
- Hardness
- 6
- Color
- Brown, tan, grey, and black banding
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, grey, and black banding. Luster: Vitreous to dull. Crystal structure: Cryptocrystalline (chalcedony/quartz). Specific gravity: 2.6-2.9.
Formation & geological history
Formed through permineralization where organic wood is replaced by minerals (usually silica) while retaining original structure. Most common in sedimentary basins from the Permian to the Neogene periods.
Uses & applications
Used in jewelry (cabochons), interior decor (bookends, tabletops), and as a popular teaching and collecting specimen.
Geological facts
Petrified wood is the state gemstone of Washington and the state fossil of North Dakota. Entire forests, like the one in Arizona, have been preserved this way over millions of years.
Field identification & locations
Identify in the field by looking for distinct tree ring patterns, bark-like textures on the exterior, and a hardness that prevents scratching by a steel knife. Commonly found in areas with past volcanic ash deposits.
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