fossil

Petrified Wood

Silicified Wood (primarily Quartz/Chalcedony, SiO2)

Hardness: 7 on the Mohs scale; Color: Brown, tan, red, yellow, grey, and black; Luster: Vitreous to dull; Crystal Structure: Microcrystalline (cryptocrystalline quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.5 - 2.7

Hardness: 7 on the Mohs scale
Color: Brown, tan, red, yellow, grey, and black
Luster: Vitreous to dull

Identified August 7, 2026More fossil →

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Physical properties

Formation & geological history

Formed when organic plant material is buried under sediment in an anoxic environment, preventing decay. Over millions of years, groundwater rich in dissolved minerals (mainly silica) flows through the sediment, replacing the organic matter cell-by-cell with minerals while preserving the original structural details. Typically dates from the Triassic period up to more recent epochs (millions of years old).

Uses & applications

Used for ornamental carvings, lapidary art, jewelry, decorative tabletops, and highly prized by fossil and rock collectors.

Geological facts

Famous occurrences include the Petrified Forest National Park in Arizona, USA, where entire ancient forests of conifer trees were buried by volcanic ash and subsequently mineralized.

Field identification & locations

Can be identified in the field by retaining the external or internal texture of wood (like tree rings or bark) while possessing the extreme hardness, weight, and conchoidal fracture of quartz. Found globally in sedimentary rock layers associated with ancient river deltas and volcanic ash beds.

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