Rock Identifier
Petrified Wood (Silicon Dioxide Fossilized Wood (SiO2)) — fossil
fossil

Petrified Wood

Silicon Dioxide Fossilized Wood (SiO2)

Hardness: 6.5 to 7 on the Mohs scale. Color: Brown, tan, cream, black, and white banding. Luster: Waxy to vitreous. Crystal Structure: Microcrystalline/Trigonal (Chalcedony/Quartz replacement). Cleavage: None, exhibits conchoidal fracture. Specific Gravity: ~2.6-2.65.

Hardness
6
Color
Brown, tan, cream, black, and white banding
Luster
Waxy to vitreous
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Physical properties

Hardness: 6.5 to 7 on the Mohs scale. Color: Brown, tan, cream, black, and white banding. Luster: Waxy to vitreous. Crystal Structure: Microcrystalline/Trigonal (Chalcedony/Quartz replacement). Cleavage: None, exhibits conchoidal fracture. Specific Gravity: ~2.6-2.65.

Formation & geological history

Formed through permineralization when organic wood material was buried rapidly under sediment or volcanic ash, deprived of oxygen, and groundwater rich in dissolved minerals (mainly silica) replaced the plant matter cell-by-cell over millions of years.

Uses & applications

Popular for lapidary work, tumbling, jewelry making, bookends, decorative carvings, and geological collections.

Geological facts

Petrified wood can retain original cellular details down to the microscopic level, allowing paleobotanists to identify tree species that lived tens to hundreds of millions of years ago.

Field identification & locations

Look for distinct grain, ring patterns, or fibrous bark-like structures preserved in hard, heavy siliceous rock. Frequently found in gravel beds, sedimentary formations, and ancient floodplains (e.g., Arizona, Washington, Madagascar).

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