fossil

Petrified Wood

Silicified Wood (primarily Chalcedony/Quartz, SiO2)

Hardness: 6.5-7 (Mohs). Color: Dark brown, black, grey with visible wood grain patterns. Luster: Vitreous to waxy after polishing. Crystal structure: Cryptocrystalline. Cleavage: None. Specific gravity: 2.58-2.91.

Hardness: 6
Color: Dark brown, black, grey with visible wood grain patterns
Luster: Vitreous to waxy after polishing

Identified July 10, 2026More fossil →

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Physical properties

Formation & geological history

Formed through permineralization, a process where organic wood materials are replaced by minerals (usually silica) while retaining the original structure. This occurs over millions of years, often dating back to the Triassic or Jurassic periods, in environments where wood was buried by volcanic ash or sediment to prevent aerobic decay.

Uses & applications

Used primarily as decorative specimens, in jewelry (cabochons), as bookends, for furniture tops, and as educational/collectible fossils.

Geological facts

Petrified wood is the state gemstone of Washington and the state rock of Mississippi. The most famous location is the Petrified Forest National Park in Arizona, which features specimens from the Late Triassic epoch.

Field identification & locations

Identify in the field by looking for rock-like hardness and density combined with visible tree rings, bark textures, or cellular wood structures. Common in sedimentary basins with a history of volcanic activity.

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