metamorphic
Petrified Wood
Silicified Wood (primarily SiO₂ - Silicon Dioxide)
Hardness: 6.5–7 on Mohs scale; Color: Mottled brown, grey, tan, and rust-orange from iron oxides; Luster: Waxy to vitreous; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.
- Hardness
- 6
- Color
- Mottled brown, grey, tan, and rust-orange from iron oxides
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Mottled brown, grey, tan, and rust-orange from iron oxides; Luster: Waxy to vitreous; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7.
Formation & geological history
Formed through the process of permineralization, where organic wood material is replaced by minerals (usually silica) over millions of years. This specimen most likely dates from the Triassic to Eocene eras (approx. 250 to 35 million years ago), occurring when logs are buried in sediment depleted of oxygen.
Uses & applications
Used primarily for decorative purposes, lapidary arts (polishing into bookends or coasters), jewelry (cabochons), and as educational or collector specimens. High-quality slabs are often used in interior design.
Geological facts
In petrified wood, the original cellular structure of the wood is often preserved in incredible detail, allowing paleobotanists to identify the species of the extinct tree. The Petrified Forest National Park in Arizona is one of the most famous global locations for these specimens.
Field identification & locations
Identify in the field by looking for distinct bark-like textures on the exterior and a heavy, stone-like weight. It will not scratch with a steel knife. Common in volcanic ash deposits or river sedimentary basins globally. Collectors should look for patterns that show growth rings or cell structures.
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