fossil

Petrified Wood

Silicified Wood (SiO2)

Hardness of 7 on the Mohs scale; colors vary from brown, red, and yellow to gray and black depending on mineral impurities; vitreous to waxy luster; microcrystalline quartz crystal structure (chalcedony/jasper); no true cleavage; specific gravity around 2.65.

Identified August 6, 2026More fossil →

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Physical properties

Formation & geological history

Formed through permineralization, where organic wood material is completely replaced by minerals (usually silica like quartz, chalcedony, or opal) over millions of years while retaining the original cellular structure. Frequently dates from the Triassic period (approx. 225 million years ago) up to more recent epochs.

Uses & applications

Used in lapidary arts, making ornamental objects, bookends, 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 from the Late Triassic epoch.

Field identification & locations

Identified in the field by its distinct wood-like grain and texture combined with a stone-like weight and hardness that can scratch glass. Found worldwide in sedimentary rock layers associated with ancient forests and volcanic ash beds.