sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5-7 Mohs; Color: Tan, brown, gray, occasionally reddish; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None; Specific Gravity: 2.6-2.9.

Hardness: 6
Color: Tan, brown, gray, occasionally reddish
Luster: Waxy to vitreous

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, brown, gray, occasionally reddish; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None; Specific Gravity: 2.6-2.9.

Formation & geological history

Formed through permineralization where organic remains are replaced by minerals (usually silica) while retaining original structure. Often dates from the Triassic to the Tertiary periods in river delta or volcanic ash environments.

Uses & applications

Used in jewelry (cabochons), interior design (tables, bookends), landscaping, and as a popular educational/collector specimen.

Geological facts

Petrified wood is the state fossil of Arizona, Mississippi, and Washington. In some cases, the replacement is so perfect that cell structures and tree rings are visible under a microscope.

Field identification & locations

Identify by looking for bark textures, growth rings, and wood grain in a piece that feels heavy and cold like stone. Common in Arizona (Petrified Forest National Park), Madagascar, and Indonesia.