Petrified Wood

Physical Properties

Hardness: 6.5-7 (Mohs scale). Color: Brown, tan, reddish-brown. Luster: Vitreous to dull. Crystal structure: Amorphous or Cryptocrystalline (Microcrystalline Quartz). Specific gravity: 2.6-2.9.

Formation & Geological History

Formed via permineralization where organic wood materials are replaced by minerals (usually silica) while retaining the original structure. Occurs in sedimentary environments, often associated with volcanic ash or alluvial deposits from the Mesozoic or Cenozoic eras.

Uses & Applications

Used for lapidary work, jewelry (cabochons), ornamental display pieces, and large-scale decorative furniture like tabletops. High value for scientific study of paleobotany.

Geological Facts

Petrified wood is the state fossil of Washington and North Dakota. It can take millions of years to form and some specimens show detailed tree rings and bark patterns.

Field Identification & Locations

Identified by wood-grain appearance combined with the density and hardness of stone. Found globally in locations like the Petrified Forest National Park (Arizona), Madagascar, and Indonesia. Field identification involves looking for cellular structure and checking for extreme hardness against steel.

Identified on: 5/20/2026

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