Rock Identifier
Petrified Wood (Silicified Wood (SiO2)) — fossil
fossil

Petrified Wood

Silicified Wood (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale. Color: Brown, tan, reddish-brown with wood grain texture. Luster: Vitreous to dull. Crystal structure: Microcrystalline quartz (chalcedony, jasper, or opal). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.

Hardness
7 on the Mohs scale
Color
Brown, tan, reddish-brown with wood grain texture
Luster
Vitreous to dull
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Physical properties

Hardness: 7 on the Mohs scale. Color: Brown, tan, reddish-brown with wood grain texture. Luster: Vitreous to dull. Crystal structure: Microcrystalline quartz (chalcedony, jasper, or opal). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.7.

Formation & geological history

Formed through permineralization when fallen trees are rapidly buried in sediment low in oxygen, preventing decay. Groundwater rich in dissolved silica flows through the organic material, replacing the original wood cell walls with silica over millions of years, often dating back to the Triassic period or earlier.

Uses & applications

Used for ornamental objects, decorative bookends, lapidary art, jewelry, and prized by fossil and mineral collectors.

Geological facts

Petrified wood can preserve microscopic cellular details of ancient plants. The famous Petrified Forest National Park in Arizona contains deposits dating back over 200 million years.

Field identification & locations

Can be identified in the field by its distinct wooden texture, weight, and lack of porosity combined with the hardness of quartz (cannot be scratched by a steel knife). Commonly found in sedimentary layers worldwide.

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