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

Petrified Wood

Silicified Wood (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7.0 (Mohs). Color: Gray, brown, tan, and reddish hues. Luster: Dull to waxy. Structure: Cryptocrystalline quartz or opal. Cleavage: None. Often retains the cellular structure of the original wood.

Hardness
6
Color
Gray, brown, tan, and reddish hues
Luster
Dull to waxy
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Physical properties

Hardness: 6.5-7.0 (Mohs). Color: Gray, brown, tan, and reddish hues. Luster: Dull to waxy. Structure: Cryptocrystalline quartz or opal. Cleavage: None. Often retains the cellular structure of the original wood.

Formation & geological history

Formed when plant material is buried by sediment and protected from decay by oxygen and organisms. Groundwater rich in dissolved solids flows through the sediment, replacing original plant material with silica, calcite, or pyrite. Usually Carboniferous to Pliocene in age.

Uses & applications

Used for decorative items, jewelry (cabochons), paperweights, landscaping, and as a popular educational/collector specimen.

Geological facts

Petrified wood is the state gemstone of Washington and the state rock of Mississippi. The process of petrifaction must happen underwater or underground to prevent the wood from rotting and allow mineralization to occur.

Field identification & locations

Identify in the field by looking for stone specimens that exhibit wood grain, bark textures, or growth rings. Found globally, with famous deposits in Arizona (USA), Madagascar, and Indonesia.

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