Mineral / Fossil

Petrified Wood

Silicified Wood (SiO2)

Hardness: 6.5–7 (Mohs scale). Color: Earthy tones (brown, yellow, red, orange) from iron oxides. Luster: Waxy to vitreous when polished. Crystal structure: Cryptocrystalline (Microcrystalline) quartz replacing organic matter. Cleavage: None, exhibits conchoidal fracture. Specific Gravity: 2.6–2.9.

Hardness: 6
Color: Earthy tones (brown, yellow, red, orange) from iron oxides
Luster: Waxy to vitreous when polished

Identified March 20, 2026More mineral / fossil →

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Physical properties

Formation & geological history

Formed via permineralization, where organic wood material is replaced by minerals (primarily silica) over millions of years after being buried in sediment/volcanic ash. Geological age ranges from the Paleozoic to the Cenozoic, commonly from the Triassic period (approx. 225 million years ago).

Uses & applications

Used in ornamental jewelry (cabochons), lapidary arts, high-end furniture (slabs for tabletops), and as decorative display specimens for collectors.

Geological facts

Petrified wood is the state stone of Washington and the state fossil of Arizona. The organic cellulose is replaced atom-by-atom by silica, often preserving the wood's microscopic cellular structure so perfectly that tree rings and bark patterns remain visible.

Field identification & locations

Identify in the field by looking for distinct wood grain patterns, growth rings, or bark textures on the exterior of a rock that feels much heavier and harder than wood. Commonly found in Arizona (Petrified Forest National Park), Oregon, Madagascar, and Indonesia. Collectors check for conchoidal fractures (glassy chips) on broken edges.