sedimentary

Petrified Wood

Silicified Wood (primarily quartz/chalcedony replacing organic wood structure, SiO2)

Hardness: 6.5-7 on the Mohs scale. Color: Brown, tan, gray, black, with occasional red, yellow, or blue hues from mineral impurities. Luster: Vitreous to dull. Crystal structure: Microcrystalline quartz (chalcedony/jasper). Cleavage: None (conchoidal fracture). Specific Gravity: 2.5-2.7.

Hardness: 6
Luster: Vitreous to dull

Identified August 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization, where organic wood is buried in an oxygen-depleted environment (such as volcanic ash or river sediments) and groundwater rich in dissolved silica slowly replaces the original cellular structure with stone over millions of years. Geological age ranges from the Triassic period to more recent epochs (millions of years old).

Uses & applications

Used for ornamental objects, high-end lapidary work, custom furniture, bookends, jewelry, and prized by fossil and rock collectors.

Geological facts

Famous occurrences include the Petrified Forest National Park in Arizona, which features massive logs from the Late Triassic period. The preservation is often so detailed that growth rings and cellular structures can be seen under a microscope.

Field identification & locations

Easily identified by its wood-like exterior texture, bark patterns, and wood grain combined with the extreme weight and hardness of stone. Commonly found in areas with ancient river floodplains or volcanic ash beds. Look for pieces displaying distinct grain and bark.

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