sedimentary

Petrified Wood

Silicified Wood (primarily SiO2 - Silicon Dioxide)

Hardness: 6.5–7 on Mohs scale; Color: Tan, brown, and ochre with wood-grain textures; Luster: Dull to waxy; Crystal structure: Cryptocrystalline (chalcedony/quartz replacement); Cleavage: Conchoidal fracture; Specific gravity: 2.6–2.9.

Hardness: 6
Color: Tan, brown, and ochre with wood-grain textures
Luster: Dull to waxy

Identified March 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via permineralization, where organic wood material is replaced by minerals (usually silica) from groundwater while buried in sediment/volcanic ash. Often dates from the Paleozoic to Cenozoic eras (millions of years old).

Uses & applications

Used for ornamental carvings, furniture (slabs), high-end jewelry (cabochons), and as museum or private geological display specimens.

Geological facts

Petrified wood is the state fossil of Arizona. The cell structure of the original tree is often preserved so perfectly that scientists can identify the species of the extinct tree under a microscope.

Field identification & locations

Identify in the field by looking for distinct bark-like textures or growth rings on a heavy, rock-hard material that will not burn or rot. Common in the Western USA (Arizona, Oregon), Madagascar, and Indonesia.

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