metamorphic
Petrified Wood
Silicified Wood (SiO2)
Hardness: 6.5–7 (Mohs scale); Color: Brown, tan, cream with visible grain; Luster: Waxy to vitreous when polished; Structure: Cryptocrystalline quartz; Cleavage: None; Specific Gravity: 2.6–2.9
- Hardness
- 6
- Color
- Brown, tan, cream with visible grain
- Luster
- Waxy to vitreous when polished
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Brown, tan, cream with visible grain; Luster: Waxy to vitreous when polished; Structure: Cryptocrystalline quartz; Cleavage: None; Specific Gravity: 2.6–2.9
Formation & geological history
Formed through permineralization where organic remains are replaced by minerals (usually silica) while retaining the original structure of the wood. Most specimens date from the Devonian to the Holocene, with many found in Triassic or Jurassic layers.
Uses & applications
Used primarily for jewelry (cabochons), lapidary art, decorative bookends, tabletops, and as geological collectibles.
Geological facts
Arizona's Petrified Forest National Park contains one of the world's largest concentrations of petrified wood. While it looks like wood, it is entirely stone; the wood fibers are replaced by quartz, jasper, and chalcedony.
Field identification & locations
Identify in the field by looking for distinct tree ring patterns, bark-like external textures, and a stone-like density. Found commonly in sedimentary basins where volcanic ash provided a source of silica after ancient floods buried forests.
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