Petrified Wood

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Brown, tan, reddish; Luster: Vitreous to dull; Crystal structure: Cryptocrystalline (Microcrystalline Quartz); Cleavage: None/Conchoidal fracture.

Formation & Geological History

Formed through permineralization where organic matter is replaced by silica (typically chalcedony or opal) in an anaerobic environment, often buried under volcanic ash or sediment millions of years ago (Mesozoic to Cenozoic eras).

Uses & Applications

Used in jewelry (lapidary), interior design (tabletops, bookends), and as a popular specimen for geological and fossil collectors.

Geological Facts

Petrified wood is the state fossil of Arizona and Washington. The cell structure of the original tree is often preserved in such detail that the species of the tree can be identified.

Field Identification & Locations

Identify in the field by looking for bark-like textures or growth rings on a stone that is significantly harder and heavier than wood. Common in the Petrified Forest National Park (Arizona) and similar arid sedimentary basins.

Identified on: 5/20/2026

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