Rock Identifier
Petrified wood (Silicified wood; commonly quartz/chalcedony (SiO₂) replacing organic tissue) — fossil
fossil

Petrified wood

Silicified wood; commonly quartz/chalcedony (SiO₂) replacing organic tissue

AI-generated identification · may be incorrect

Brown, wood-grained fossil with dull to waxy luster; hardness about 6.5–7 Mohs, no prominent cleavage, and quartz-like density (~2.6 g/cm³). Visible bands and fibrous textures preserve the original growth structure.

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Physical properties

Brown, wood-grained fossil with dull to waxy luster; hardness about 6.5–7 Mohs, no prominent cleavage, and quartz-like density (~2.6 g/cm³). Visible bands and fibrous textures preserve the original growth structure.

Formation & geological history

Formed when buried wood was gradually replaced by silica-rich groundwater while retaining cellular detail, typically during the Cenozoic or older. It occurs in volcanic ash beds, floodplains, and sedimentary deposits.

Uses & applications

Used as a lapidary material for cabochons, carvings, bookends, and decorative slices; attractive pieces are collected rather than used structurally.

Geological facts

Petrified wood is a fossil, not technically a rock type in the igneous/sedimentary/metamorphic classification. Color may result from iron, manganese, or other trace-element impurities.

Field identification & locations

Identify it by recognizable wood grain, bark or growth rings, high hardness, and silica-like fracture; it commonly occurs in Arizona, Wyoming, Indonesia, Madagascar, and Australia. A definitive test is hardness and microscopic cellular structure.

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