fossil

Petrified Wood

Silicified Wood (SiO2)

Hardness of 6.5 to 7 on the Mohs scale; varies in color from brown, red, and yellow to black depending on mineral impurities like iron oxides; vitreous to waxy luster; amorphous crystal structure as quartz replaces organic cellular material; specific gravity of 2.5 to 2.7.

Identified July 29, 2026More fossil →

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Physical properties

Formation & geological history

Formed through the process of permineralization, where organic wood material is buried under sediment in anoxic conditions and gradually replaced by silica-rich groundwater over millions of years (typically dating from the Triassic to Tertiary periods, spanning tens to hundreds of millions of years ago).

Uses & applications

Used in lapidary arts, making jewelry, decorative ornamental carvings, bookends, table tops, and as valuable specimens for fossil and mineral collectors.

Geological facts

Famous localities include the Petrified Forest National Park in Arizona, USA, which features massive fallen logs from the Late Triassic period preserved in vibrant colors due to trace iron and manganese.

Field identification & locations

Can be identified in the field by its distinct wood-like exterior texture and growth rings combined with an unusually heavy weight, cold touch, and a conchoidal fracture typical of quartz.