sedimentary

Petrified Wood

Silicified Wood (primarily SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Brown, tan, reddish-brown. Luster: Waxy to vitreous when polished, dull or earthy when raw. Structure: Shows original organic cellular structure preserved in microcrystalline quartz. Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Brown, tan, reddish-brown
Luster: Waxy to vitreous when polished, dull or earthy when raw

Identified April 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization, where organic remains are replaced by minerals (usually silica) while retaining the original structure. This typically occurs when wood is buried under sediment/volcanic ash, depriving it of oxygen and allowing mineral-rich water to seep in. Ages range from the Devonian to the Pleistocene (hundreds of millions of years old).

Uses & applications

Used in ornamental jewelry (cabochons), interior design (furniture, bookends, tiles), and as popular specimens for geological collectors.

Geological facts

Petrified wood is the state gemstone of Washington and the state fossil of Arizona. In some locations, like the Petrified Forest National Park, entire logs have turned into solid quartz and chalcedony.

Field identification & locations

Identify in the field by looking for distinct wood-grain patterns, growth rings, or bark-like textures on a rock that is too hard to scratch with a steel knife. Commonly found in areas with historic volcanic activity or ancient floodplains like the American Southwest and Indonesia.