fossil

Petrified Wood

Silicified Wood / Xylopal (SiO2)

Mohs hardness of 6.5 to 7; colors include brown, grey, black, red, and yellow due to mineral impurities; vitreous to waxy luster; amorphous crystal structure (microcrystalline quartz/chalcedony); conchoidal fracture with no true cleavage; specific gravity around 2.5 to 2.7.

Identified August 1, 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, opal, or chalcedony) over millions of years, often dating from the Triassic period or younger, buried under volcanic ash or sediment lacking oxygen.

Uses & applications

Used for ornamental objects, decorative bookends, lapidary art, jewelry, furniture, and highly valued as collector specimens.

Geological facts

Petrified wood can preserve the fine cellular structure of ancient trees down to the microscopic level, revealing details of prehistoric forests that grew tens or hundreds of millions of years ago. Arizona's Petrified Forest National Park contains some of the world's most famous deposits.

Field identification & locations

Identified in the field by its distinct tree bark-like exterior texture combined with the heavy weight and cold, smooth, stone-like interior that shows growth rings. Commonly found in areas with ancient sedimentary layers and volcanic deposits, such as the American Southwest.