metamorphic
Petrified Wood
Silicified Wood (SiO2)
Hardness: 6.5-7 on the Mohs scale. Color: Tan, brown, and ochre with wood grain texture. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.9.
- Hardness
- 6
- Color
- Tan, brown, and ochre with wood grain texture
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on the Mohs scale. Color: Tan, brown, and ochre with wood grain texture. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.9.
Formation & geological history
Formed through permineralization, a process where organic material is replaced by minerals (usually silica) while retaining original anatomical structure. This occurs when wood is buried in sediment or volcanic ash, protecting it from decay. Specimens can range from 20 to 300 million years old.
Uses & applications
Commonly used for lapidary work, jewelry (cabochons), interior design (furniture or bookends), and museum/educational displays.
Geological facts
All the organic matter has been replaced by minerals while keeping the delicate structures like growth rings intact. The color is often determined by trace elements: iron produces reds and yellows, while manganese produces pinks and purples.
Field identification & locations
Identify in the field by looking for 'rock that looks like wood' but is heavy and cold to the touch. Common locations include the Petrified Forest National Park (Arizona), Madagascar, and Indonesia. Collectors look for high contrast in grain and minimal cracking.
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