metamorphic
Petrified Wood
Silicified Wood (SiO2)
Hardness: 6.5–7 (Mohs); Color: Shades of brown, gray, and tan; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (Microcrystalline Quartz); Cleavage: None; Specific Gravity: 2.6–2.9
- Hardness
- 6
- Color
- Shades of brown, gray, and tan
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5–7 (Mohs); Color: Shades of brown, gray, and tan; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (Microcrystalline Quartz); Cleavage: None; Specific Gravity: 2.6–2.9
Formation & geological history
Formed through permineralization, where organic wood material is replaced by silica-rich minerals (quartz or chalcedony) over millions of years; typically found in Triassic to Tertiary deposits (200 to 2 million years old) in sedimentary basins.
Uses & applications
Used in ornamental jewelry (cabochons), interior decor (bookends, tabletops), landscaping, and as a popular focus for geological collectors.
Geological facts
Petrified wood is the state gem of Washington and the state fossil of Arizona; the process happens under anaerobic conditions, preserving tree rings and even cellular structures perfectly in stone.
Field identification & locations
Identify in the field by looking for bark-like textures, tree ring patterns, or a wood grain appearance on a heavy, rock-hard specimen. Commonly found in old river beds and badlands like the Petrified Forest National Park (USA), Madagascar, and Indonesia.
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