sedimentary

Petrified Wood

Silicified Wood (primarily Quartz/Chalcedony, formula SiO2)

Hardness: 6.5-7 (Mohs); Color: Tan, white, gray, and black; Luster: Waxy to vitreous; Structure: Microcrystalline (retains original cellular structure of wood); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9

Hardness: 6
Color: Tan, white, gray, and black
Luster: Waxy to vitreous

Identified May 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through permineralization when woody plant material is buried by sediment and saturated with mineral-rich groundwater. Over millions of years (typically Triassic to Neogene periods), silica replaces the organic material molecule by molecule.

Uses & applications

Used primarily for lapidary work, jewelry making (cabochons), interior decor (tabletops, bookends), and as high-value geological collectibles.

Geological facts

Many specimens are so well-preserved that they show individual tree rings and cellular bark details. The most famous location is the Petrified Forest National Park in Arizona, which contains wood mostly from the Triassic period (~225 million years ago).

Field identification & locations

Identify in the field by looking for a combination of rock-hard weight/texture and visible wood-grain patterns. Commonly found in areas with volcanic ash and ancient riverbeds. For collectors, look for high-contrast colors and intact bark structures.

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