Petrified Wood

Physical Properties

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, cream, and grey with distinct wood-grain banding; Luster: Waxy or vitreous; Crystal structure: Cryptocrystalline (Microcrystalline Quartz); Specific Gravity: 2.6-2.9

Formation & Geological History

Formed through permineralization where organic wood material is replaced by minerals, typically silica (quartz), in the absence of oxygen. Often found in volcanic ash layers or river sediments dating back millions of years (commonly Carboniferous to Triassic periods).

Uses & Applications

Used primarily for semi-precious jewelry (cabochons), lapidary art, home decor (coasters, bookends), and as collector specimens.

Geological Facts

Petrified wood is the state fossil of Washington and Arizona. Some of the most famous specimens are found in the Petrified Forest National Park in Arizona, which contains wood that is over 200 million years old.

Field Identification & Locations

Identify in the field by looking for rock specimens that retain the cellular structure, rings, or bark textures of a tree. Common in sedimentary basins with high silica groundwater. Tips: check for a hardness that can scratch glass.

Identified on: 4/25/2026

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