Petrified Wood

Physical Properties

Hardness: 6.5–7 (Mohs scale); Color: Brown, tan, cream, potentially reddish from iron oxides; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Microcrystalline quartz); Cleavage: None; Specific Gravity: 2.6–2.9

Formation & Geological History

Formed via permineralization where organic wood materials are replaced by minerals (usually silica) while retaining original structure. Most found specimens date back to the Triassic or Jurassic periods (over 200 million years ago) in fluvial or volcanic ash environments.

Uses & Applications

Used in lapidary work, jewelry making (cabochons), interior design (tabletops/bookends), and as an educational geological specimen.

Geological Facts

Famous locations like the Petrified Forest National Park in Arizona contain entire downed trees turned to stone. In some rare cases, the replacement is so perfect that cell structures and growth rings can be seen under a microscope.

Field Identification & Locations

Identify by looking for wood-like grain, bark-like texture, and growth rings in a heavy, stony material that cannot be scratched by a steel knife. Common in areas with historical volcanic activity or ancient river beds.

Identified on: 4/14/2026

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