sedimentary
Petrified Wood
Silicified Wood (primarily SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-brown, and earthy tones; Luster: Waxy to dull (vitreous when polished); Crystal Structure: Cryptocrystalline (Microcrystalline Quartz/Chalcedony); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.9
- Hardness
- 6
- Color
- Brown, tan, reddish-brown, and earthy tones
- Luster
- Waxy to dull (vitreous when polished)
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish-brown, and earthy tones; Luster: Waxy to dull (vitreous when polished); Crystal Structure: Cryptocrystalline (Microcrystalline Quartz/Chalcedony); 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) in the absence of oxygen, often buried by volcanic ash or river sediments. Aging can range from the Devonian period through the Pleistocene.
Uses & applications
Used primarily for jewelry (cabochons), lapidary art, decorative bookends, furniture tops, and architectural accents. It is also highly valued as a geological teaching specimen.
Geological facts
Petrified wood is the state fossil of Arizona. While it looks like wood, it contains no original organic material; it is a three-dimensional stone replica of the original tree structure, sometimes preserving cellular detail.
Field identification & locations
Identify in the field by looking for distinct bark-like textures, tree rings, and a weight much heavier than modern wood. Commonly found in the American Southwest (Arizona), Madagascar, and Indonesia. Collectors look for pieces with 'bark' intact.
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