sedimentary

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Gray, tan, brown, or white; Lustre: Dull to waxy; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Specific Gravity: 2.6–2.9.

Hardness: 6
Color: Gray, tan, brown, or white

Identified April 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5–7 on Mohs scale; Color: Gray, tan, brown, or white; Lustre: Dull to waxy; Crystal structure: Microcrystalline (Cryptocrystalline) quartz; Specific Gravity: 2.6–2.9.

Formation & geological history

Formed through permineralization, a process where organic material is replaced by minerals (usually silica) while retaining the original structure of the wood. Most specimens range from 20 to 300 million years old (Triassic to Neogene periods).

Uses & applications

Used primarily for decorative purposes, jewelry (cabochons), furniture (tabletops), and as educational or geological collectibles.

Geological facts

Famous locations like the Petrified Forest National Park in Arizona feature logs that are over 200 million years old. Unlike most fossils, petrified wood preserves the cellular structure of the original plant, allowing scientists to identify the species of tree.

Field identification & locations

Identify in the field by looking for bark-like textures on the exterior and growth rings in the cross-section. It is often much heavier and harder than regular wood. Common in volcanic ash deposits or sedimentary river basins.