metamorphic
Petrified Wood
Silicified Wood (primarily Quartz / Chalcedony: SiO2)
Hardness: 7.0 on Mohs scale; Color: Variable (reds, tans, browns, blacks, grays); Luster: Vitreous to waxy; Structure: Pseudomorphous (internal wood grain, rings, and bark textures preserved by silica); Opaque to translucent; Specific Gravity: 2.6–2.9.
- Hardness
- 7
- Color
- Variable (reds, tans, browns, blacks, grays)
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7.0 on Mohs scale; Color: Variable (reds, tans, browns, blacks, grays); Luster: Vitreous to waxy; Structure: Pseudomorphous (internal wood grain, rings, and bark textures preserved by silica); Opaque to translucent; Specific Gravity: 2.6–2.9.
Formation & geological history
Formed through permineralization over millions of years (typically 20-300 million years old). Organic material is replaced by minerals like silica, calcite, or pyrite while buried under sediment/volcanic ash, depriving it of oxygen and preventing rot.
Uses & applications
Used for ornamental furniture (tabletops), lapidary work (jewelry, cabochons, bookends), landscaping, and as a highly sought-after specimen for geological collectors.
Geological facts
The largest concentration is in Petrified Forest National Park, Arizona. It provides a unique biological record of extinct flora. Each color represents a trace element: iron causes reds/oranges, manganese creates purples/blacks, and copper/cobalt create blues/greens.
Field identification & locations
Identify in the field by looking for rock-hard specimens with distinct bark textures, growth rings, or wood-like fractures and grain. Commonly found in sedimentary basins or areas with historical volcanic activity. Note: Collecting on US federal lands is strictly regulated or illegal.
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