mineral

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5–7 on the Mohs scale. Color: Tan, brown, grey, and black with visible wood grain rings. Luster: Vitreous to waxy. Crystal Structure: Cryptocrystalline (usually chalcedony/quartz). Cleavage: None; conchoidal fracture. Specific Gravity: 2.6–2.9.

Hardness: 6
Color: Tan, brown, grey, and black with visible wood grain rings
Luster: Vitreous to waxy

Identified March 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed through permineralization when woody debris is buried under sediment (volcanic ash or river silt) and groundwater rich in dissolved silica replaces the organic matter cell-by-cell. This specimen likely dates from the Triassic to the Pleistocene epochs.

Uses & applications

Used primarily for display specimens, lapidary work (jewelry, bookends), and ornamental landscaping. Higher quality pieces are prized by geological collectors.

Geological facts

Petrified wood is the state fossil of Arizona, North Dakota, and Louisiana. Despite being a 'rock,' it retains the original anatomy of the tree, including growth rings and cellular structures that can sometimes be identified under a microscope.

Field identification & locations

Identify by looking for concentric bark-like patterns and growth rings on the cross-section. It feels much heavier and cooler to the touch than real wood. Commonly found in areas with past volcanic activity like Arizona (USA), Madagascar, and Brazil.