Rock Identifier
Petrified Wood (Silicified wood (Quartz / Chalcedony replacement of organic cellulose)) — fossil
fossil

Petrified Wood

Silicified wood (Quartz / Chalcedony replacement of organic cellulose)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale; Color: Varies widely including red, yellow, brown, orange, and black depending on mineral impurities; Luster: Vitreous to dull; Crystal structure: Microcrystalline (quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7

Hardness
7 on the Mohs scale
Luster
Vitreous to dull
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Physical properties

Hardness: 7 on the Mohs scale; Color: Varies widely including red, yellow, brown, orange, and black depending on mineral impurities; Luster: Vitreous to dull; Crystal structure: Microcrystalline (quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7

Formation & geological history

Formed when ancient trees are rapidly buried in low-oxygen, sediment-rich environments such as river floodplains or volcanic ash beds, allowing groundwater rich in dissolved silica to slowly replace the organic cellular structure with minerals over millions of years (often Triassic to Jurassic periods).

Uses & applications

Used for ornamental purposes, decorative objects, bookends, lapidary art, jewelry, and prized by fossil and mineral collectors.

Geological facts

Famous occurrences include the Petrified Forest National Park in Arizona, which contains logs dating back over 200 million years. The original cellular structure is often so well-preserved that growth rings and cell walls can be viewed under a microscope.

Field identification & locations

Identified in the field by its distinct wood-like exterior texture combined with a heavy, stone-like weight and cold feel. Common locations include western United States, Argentina, and various desert regions worldwide.

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