sedimentary
Petrified Wood
Silicified wood (Quartz/Chalcedony replacement) SiO2
Hardness: 6.5-7 (Mohs); Color: Red, brown, tan, and cream due to iron oxides; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9
- Hardness
- 6
- Color
- Red, brown, tan, and cream due to iron oxides
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Red, brown, tan, and cream due to iron oxides; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9
Formation & geological history
Formed through permineralization where organic remains are replaced by minerals (usually silica) from groundwater while keeping the original structure. Common in the Triassic and Cenozoic eras, often in areas covered by volcanic ash or sedimentary basins.
Uses & applications
Used for jewelry (cabochons), lapidary art, decorative bookends, furniture tops, and as a popular specimen for geological collections.
Geological facts
The entire process takes millions of years. Famous locations include the Petrified Forest National Park in Arizona, USA. It is theoretically a fossil as much as it is a rock.
Field identification & locations
Identify by looking for bark-like textures or visible growth rings preserved in stone. It is commonly found in areas of ancient floodplains or near volcanic beds. Collectors should look for vibrant colors and fine anatomical preservation.
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