sedimentary
Petrified Wood
Silicified wood (principally SiO2)
Hardness: 7 on Mohs scale; Color: Brown, grey, tan; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None, conchoidal fracture; Specific gravity: 2.6-2.9
- Hardness
- 7 on Mohs scale
- Color
- Brown, grey, tan
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Brown, grey, tan; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: None, conchoidal fracture; Specific gravity: 2.6-2.9
Formation & geological history
Formed through permineralization where organic wood materials are replaced by minerals (usually silica) while retaining the original wood structure. This process occurs underground under sediment, often over millions of years (commonly Mesozoic to Cenozoic eras).
Uses & applications
Used primarily for ornamental purposes, jewelry (cabochons), interior design (tabletops), and as highly collectible geological specimens.
Geological facts
Petrified wood is the state gemstone of Arizona. The cell structure of the original tree is often so well preserved that the species of the tree can be identified under a microscope.
Field identification & locations
Identify by looking for visible tree rings or bark-like textures on the exterior. It is much heavier and harder than normal wood. Common locations include Arizona (Petrified Forest National Park), Madagascar, and Indonesia.
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