metamorphic
Petrified Wood
Silicified Wood (primarily SiO2 - Silicon Dioxide / Chalcedony)
Hardness: 6.5–7 on Mohs scale; Color: Gray, brown, and tan with visible wood grain patterns; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.91.
- Hardness
- 6
- Color
- Gray, brown, and tan with visible wood grain patterns
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Gray, brown, and tan with visible wood grain patterns; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.58–2.91.
Formation & geological history
Formed through the process of permineralization where organic wood material is replaced by minerals (usually silica) from groundwater while keeping the cellular structure intact. This occurs in oxygen-deficient environments like volcanic ash beds or river sediments over millions of years (typically Mesozoic to Cenozoic eras).
Uses & applications
Used in high-end furniture (tabletops), lapidary work (cabochons, bookends), landscaping, and as prized specimens for geological collectors.
Geological facts
Petrified wood is the state gemstone of Washington and the state rock of Mississippi. The famous Petrified Forest National Park in Arizona contains wood from the Triassic period, approximately 225 million years old.
Field identification & locations
Identify by looking for distinct 'growth rings,' bark textures, or woody fibers preserved in a stone that cannot be scratched by a steel knife. Commonly found in areas with historical volcanic activity or ancient fluvial basins like the American West (Arizona, Oregon, Washington).
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