Petrified Wood

Physical Properties

Hardness: 6.5–7 on Mohs scale. Color: Brown, tan, reddish, and black streaks. Luster: Vitreous to waxy. Structure: Cryptocrystalline (replacing original plant cell structure). Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.9.

Formation & Geological History

Formed when plant material is buried by sediment and protected from decay by oxygen and organisms. Mineral-rich groundwater flows through the sediment, replacing original organic material with silica, calcite, or pyrite. Usually several million years old, often from the Triassic or Cenozoic periods.

Uses & Applications

Used primarily for lapidary work (jewelry, cabochons), home decor (bookends, table tops), and as collector specimens.

Geological Facts

Famous locations include the Petrified Forest National Park in Arizona. Because the mineralization often follows the original cellular structure of the wood, growth rings and bark textures can often be perfectly preserved in stone.

Field Identification & Locations

Identify in the field by looking for wood-like grain patterns, bark-like exterior textures, and a hardness that prevents scratching with a steel knife. Commonly found in areas with historic volcanic activity and sedimentary basins.

Identified on: 4/25/2026

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