Petrified Wood

Physical Properties

Hardness: 6.5–7 on Mohs scale; Color: Browns, tans, and grays with visible wood grain; Luster: Vitreous to waxy; Structure: Cryptocrystalline (chalcedony/quartz); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6–2.9.

Formation & Geological History

Formed through the process of permineralization where organic wood material is replaced by minerals (usually silica) from groundwater while buried under sediment or volcanic ash. This typically occurs over millions of years, often dating back to the Triassic or Jurassic periods.

Uses & Applications

Used primarily for ornamental items, jewelry (cabochons), lapidary art, furniture cross-sections, and as a popular collectible for geological enthusiasts.

Geological Facts

Petrified wood is the state gemstone of Washington and the state fossil of Arizona. Large concentrations are found in the Petrified Forest National Park, many of which are from the Triassic period, approximately 225 million years old.

Field Identification & Locations

Identify in the field by looking for bark textures, growth rings, or woody fibers preserved in a stony medium. Common in badlands and areas with ancient river deposits. Collectors should look for high-contrast color and preservation of internal cell structures.

Identified on: 4/13/2026

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