fossil

Petrified Wood

Silicon Dioxide (SiO2)

Hardness: 6.5–7 (Mohs scale); Color: Brown, red, yellow, tan, gray; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline (usually chalcedony or opal replacing organic matter); Specific Gravity: 2.6–2.9

Hardness: 6
Color: Brown, red, yellow, tan, gray
Luster: Vitreous to waxy

Identified July 4, 2026More fossil →

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Physical properties

Formation & geological history

Formed through permineralization when wood is buried under sediment or volcanic ash, excluding oxygen and allowing mineral-rich water to replace organic cells with silica or calcite over millions of years, often dating to the Triassic or Cenozoic eras.

Uses & applications

Used in high-end jewelry (cabochons), lapidary art, furniture (tabletops), interior design, and as educational fossil specimens for collectors.

Geological facts

In petrified wood, the original cellular structure of the tree is often perfectly preserved in stone. Arizona's Petrified Forest National Park contains one of the world's largest concentrations of these ancient trees, dating back about 225 million years.

Field identification & locations

Identify in the field by looking for 'rock' that retains the bark texture or concentric tree-ring patterns; it is significantly heavier than wood. Common in areas with ancient volcanic activity or river basins, such as the American Southwest, Indonesia, and Madagascar.