fossil

Petrified Wood

Silicified wood (primarily quartz, SiO2)

Hardness: 6.5-7 on the Mohs scale; Color: varies widely including brown, grey, red, yellow, and black depending on mineral impurities; Luster: vitreous to waxy; Crystal structure: microcrystalline quartz (chalcedony/jasper); Specific gravity: 2.5-2.7

Hardness: 6
Luster: vitreous to waxy

Identified August 7, 2026More fossil →

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Physical properties

Formation & geological history

Forms when fallen trees are rapidly buried in sediment-rich, oxygen-poor environments such as riverbeds or volcanic ash flows, preventing decay. Over millions of years, groundwater rich in dissolved silica replaces the organic plant material cell-by-cell with mineral deposits, often dating from the Triassic period or younger.

Uses & applications

Used for ornamental carvings, high-end lapidary work, decorative tabletops, jewelry, and prized by fossil and mineral collectors.

Geological facts

Famous occurrences include the Petrified Forest National Park in Arizona, which contains logs dating back over 200 million years to the Late Triassic period. The preservation can be so detailed that annual growth rings and cellular structures remain visible under a microscope.

Field identification & locations

Can be identified in the field by its wood-like exterior texture and bark patterns combined with a stone-like weight, cold feel, and conchoidal fracture. Found worldwide in sedimentary strata, particularly in regions with ancient river systems or volcanic activity.

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