metamorphic
Petrified Wood
Silicified Wood (SiO2)
Hardness: 6.5-7.0 on Mohs scale; Color: Brown, tan, cream, with dark grey banding; Luster: Waxy to vitreous; Crystal structure: Microcrystalline quartz (Trigonal); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.9
- Hardness
- 6
- Color
- Brown, tan, cream, with dark grey banding
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7.0 on Mohs scale; Color: Brown, tan, cream, with dark grey banding; Luster: Waxy to vitreous; Crystal structure: Microcrystalline quartz (Trigonal); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.9
Formation & geological history
Formed through the process of permineralization where organic wood material is replaced by silica (chalcedony or opal) in anaerobic conditions, often under volcanic ash or sediment. Geological ages vary, commonly from the Triassic through the Cenozoic.
Uses & applications
Used primarily for lapidary work, jewelry (cabochons), ornamental display pieces, furniture (large slabs), and as a popular collector's item.
Geological facts
Petrified wood is the state gem of several US states including Washington and Arizona. While it looks like wood, it contains no original organic matter; it is essentially a quartz cast of the original tree's cellular structure.
Field identification & locations
Identify by looking for preserved wood grain, bark textures, or annual growth rings within a heavy, stone-like material. Often found in dry, eroded landscapes or riverbeds in areas like Arizona, Madagascar, and Indonesia.
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