metamorphic
Petrified Wood
Silicified Wood (SiO2)
Hardness: 6.5–7 on Mohs scale; Color: Brown, tan, black, and cream with visible wood grain; Luster: Waxy to vitreous (glassy) when polished; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.9.
- Hardness
- 6
- Color
- Brown, tan, black, and cream with visible wood grain
- Luster
- Waxy to vitreous (glassy) when polished
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Physical properties
Hardness: 6.5–7 on Mohs scale; Color: Brown, tan, black, and cream with visible wood grain; Luster: Waxy to vitreous (glassy) when polished; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.9.
Formation & geological history
Formed through permineralization, where organic wood material is replaced by minerals (usually silica) while retaining the original cellular structure. This occurs over millions of years (often Triassic or Jurassic periods) when wood is buried under sediment and volcanic ash in an anaerobic environment.
Uses & applications
Commonly used in jewelry, lapidary arts, interior decoration (tabletops, bookends), and as collectible educational specimens.
Geological facts
Petrified wood is the state stone of Arizona, home to the Petrified Forest National Park. Some specimens are so perfectly preserved that individual tree rings and cell walls can be viewed under a microscope.
Field identification & locations
Identify in the field by looking for distinct bark-like textures or growth rings on the exterior of a rock that otherwise feels like glass or quartz. Commonly found in areas with historic volcanic activity and sedimentary basins, such as the American Southwest, Argentina, and Egypt.
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