fossil

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Brown, tan, cream, and beige with visible grain patterns, Luster: Vitreous to waxy, Crystal structure: Hexagonal (cryptocrystalline), Cleavage: None/Conchoidal fracture.

Hardness: 6

Identified July 8, 2026More fossil →

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Physical properties

Formation & geological history

Formed during the permineralization process where organic wood materials are replaced by silica (calcedony or quartz) by groundwater over millions of years, often from the Mesozoic or Cenozoic eras.

Uses & applications

Used for jewelry (cabochons), lapidary art, decorative bookends, home decor, and as a popular teaching fossil for education and collections.

Geological facts

Petrified wood is the state gem of Washington and the state fossil of Arizona. The organic cellulose is replaced by minerals while keeping the original structure of the wood cells intact.

Field identification & locations

Identified by wood-like texture or growth rings combined with the weight and hardness of stone. Found globally in areas like the Petrified Forest National Park in Arizona, USA, or Madagascar. To identify, look for parallel grain lines and lack of splintering.