mineral

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Variegated shades of brown, tan, gray, and cream with possible banding; Luster: Dull to vitreous/waxy; Crystal Structure: Microcrystalline (Cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.9

Hardness: 6
Luster: Dull to vitreous/waxy

Identified May 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed through permineralization, a process where organic material is replaced by minerals (usually silica) while retaining the wood's original structure. This typically occurs when wood is buried under sediment or volcanic ash in an anaerobic environment. Specimens can be millions of years old, often dating to the Cretaceous or Cenozoic periods.

Uses & applications

Used primarily in lapidary arts, jewelry (cabochons), ornamental home decor (bookends, tabletops), and as geological collector specimens.

Geological facts

Petrified wood is the state rock of Mississippi and the state gemstone of Washington. Famous locations include the Petrified Forest National Park in Arizona, which features some of the largest logs in the world.

Field identification & locations

Identify in the field by looking for wood-like textures such as bark patterns and growth rings in a heavy, stony material that cannot be scratched by a steel knife. Commonly found in sedimentary basins and areas with historical volcanic activity.