sedimentary

Petrified Wood

Silicon Dioxide (SiO2) - Calcified / Silicified Wood

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: Brown, red, grey, or purple (depending on mineral impurities), Luster: Vitreous to dull, Crystal Structure: Cryptocrystalline (Microcrystalline quartz), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6-2.9

Hardness: 6

Identified February 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization or replacement where organic material is buried under sediment and water-saturated with silica replaces the plant cells over millions of years (typically Triassic to Neogene periods).

Uses & applications

Used in lapidary arts, jewelry (cabochons), ornamental furniture (tabletops), and highly valued by fossil and mineral collectors.

Geological facts

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

Field identification & locations

Identify in the field by looking for wood-like grain patterns, growth rings, or bark textures on a stone that is too hard to scratch with steel. Commonly found in eroded badlands and volcanic ash deposits.