sedimentary

Petrified Wood

Silicified Wood (primarily SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Tan, brown, and grey with wood-like grain; Luster: Vitreous to waxy; Crystal structure: Trigonal/Cryptocrystalline (Chalcedony/Quartz); Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Tan, brown, and grey with wood-like grain
Luster: Vitreous to waxy

Identified June 8, 2026More sedimentary →

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Physical properties

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 the original plant material with silica, calcite, or pyrite over millions of years. Usually from the Permian through the Cenozoic era.

Uses & applications

Used in lapidary work for jewelry, bookends, coffee tables, and garden ornaments. Highly valued by fossil and mineral collectors for aesthetic and educational purposes.

Geological facts

Unlike a cast or mold, petrified wood is a three-dimensional replacement of the original organic material, often preserving cellular details of the tree tissue. The largest concentration in the world is found in the Petrified Forest National Park in Arizona.

Field identification & locations

Identify by looking for wood-grain patterns, bark textures, or annual growth rings in a heavy, stony material. Found commonly in areas with volcanic ash and sedimentary deposits. Collectors should look for pieces with well-preserved grain or vibrant colors.