sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
Hardness: 6.5-7 (Mohs); Color: Brown, tan, reddish-brown; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.9
- Hardness
- 6
- Color
- Brown, tan, reddish-brown
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Brown, tan, reddish-brown; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.9
Formation & geological history
Formed when organic plant material is buried by sediment (often volcanic ash) and water rich in dissolved minerals (silica) flows through it, replacing original cells with stone. Usually 20 to 200 million years old.
Uses & applications
Used in jewelry (cabochons), interior design (polished slabs, tabletops), landscape architecture, and as educational fossils.
Geological facts
Unlike many fossils, petrified wood is 3D and preserves fine biological details like growth rings and cell structure. The most famous location is Petrified Forest National Park in Arizona.
Field identification & locations
Identified by wood-like texture or grain on the surface but with the hardness and weight of stone. Found in ancient riverbeds and volcanic ash deposits. Collectors look for vibrant colors and distinct ring patterns.
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