Mineral / Fossil
Petrified Wood
Silicified Wood (SiO2 - Quartz/Chalcedony replacement)
Hardness: 6.5–7 on the Mohs scale. Color: Brown, tan, and gray bands. Luster: Waxy to dull. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.9.
- Hardness
- 6
- Color
- Brown, tan, and gray bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5–7 on the Mohs scale. Color: Brown, tan, and gray bands. Luster: Waxy to dull. Crystal Structure: Hexagonal (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 silica-rich water over millions of years, often in volcanic ash deposits. Common specimens range from the Triassic (225 million years) to the Pliocene.
Uses & applications
Used for lapidary work, jewelry, home decor (tabletops, bookends), and as highly sought-after geological collectibles.
Geological facts
Petrified wood is a fossil in which all the organic materials have been replaced with minerals while retaining the original structure of the wood, including growth rings and cellular detail. It is the state gem of Washington and the state fossil of Arizona.
Field identification & locations
Identify by looking for wood-like grain patterns, tree rings, and bark-like textures on the exterior. It is commonly found in badlands, desert regions, and areas with historic volcanic activity like the Southwest USA and Madagascar.
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