mineral

Petrified Wood (Silicified Wood)

Silicified Wood (primarily Chalcedony/Quartz, SiO2)

Hardness: 6.5–7 (Mohs scale); Color: White, tan, brown, and reddish-orange due to iron oxides; Luster: Waxy to vitreous; Structure: Microcrystalline (trigonal); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.9.

Hardness: 6
Color: White, tan, brown, and reddish-orange due to iron oxides
Luster: Waxy to vitreous

Identified March 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed via permineralization where organic wood materials are replaced by silica (chalcedony or opal) from groundwater. This specimen appears to be from the Cenozoic or Mesozoic eras (approx. 20–225 million years old), typically forming in fluvial (river) environments or after volcanic ash falls.

Uses & applications

Used primarily for decorative purposes, jewelry (cabochons), bookends, furniture tops, and as educational/geological collectibles.

Geological facts

Petrified wood is the state fossil of Arizona. The process happens without oxygen, preventing rot while crystals grow. In some cases, even the individual cell structures and growth rings of the original tree are visible under magnification.

Field identification & locations

Identify in the field by looking for bark-like textures on the exterior and a smooth, glass-like fracture on the interior. Often found in badlands or areas with high erosion. Significant deposits are in Arizona (USA), Madagascar, and Indonesia.

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