Petrified Wood (Silicified Fossil)

Physical Properties

Hardness: 6.5-7 (Mohs scale), Color: Brown, gray, tan with wood-grain texture, Luster: Dull to waxy, Structure: Cryptocrystalline quartz (Chalcedony/Agate) replacing organic cellulose.

Formation & Geological History

Formed when plant material is buried by sediment and protected from decay by oxygen. Groundwater rich in dissolved solids (silica) flows through the sediment, replacing original organic material with silica over millions of years, typically during the Mesozoic or Cenozoic eras.

Uses & Applications

Used for decorative ornaments, jewelry (cabochons), furniture (slices for tabletops), and as a popular geological collecting specimen.

Geological Facts

The entire process can take millions of years. It is essentially a 3D stone model of the original tree. Famous locations include the Petrified Forest National Park in Arizona.

Field Identification & Locations

Identify in the field by looking for bark textures, growth rings, or wood-like fibers on an object that feels like stone. It will not scratch with a pocket knife. Commonly found in riverbeds or badlands where ancient volcanic ash deposits were present.

Identified on: 4/20/2026

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