Petrified Wood
Petrified wood forms when buried plant material is replaced by silica-rich groundwater over millions of years — molecule by molecule — preserving the original wood structure in mineral form. The Chinle Formation in Arizona preserves trees from the Triassic period (225 million years ago). Commercial collecting is legal on adjacent BLM land; the National Park itself prohibits collecting.
Physical Properties
Chemical Formula
SiO₂ (replaced wood — chalcedony/quartz)
Hardness (Mohs)
6.5–7
Color
Brown, red, yellow, white, gray — wood grain pattern preserved
Luster
Waxy to dull
Crystal System
Microcrystalline (chalcedony)
Streak
White
Cleavage
None
Specific Gravity
2.58–2.91
🔍 Field Identification Tips
Preserved wood grain, growth rings, and bark texture are unmistakable. Hardness 6.5–7 (much harder than real wood). Takes a high polish. Arizona petrified wood often shows brilliant reds and oranges from iron oxide. Opalescent varieties from Nevada show play-of-color.
Varieties & Forms
📍 Where to Find Petrified Wood in the US
Uses & Applications
Lapidary, polished slabs, decorative furniture tops, bookends, jewelry.
💰 Collector Value Guide
Small Arizona pieces: $2–$20/lb. Cut/polished slabs: $20–$500. Opalescent petrified wood: $50–$2,000. Display-grade logs: $500–$10,000.
Find Petrified Wood With Our Tools
Use the We Lick Rocks app to identify specimens, find dig sites, and connect with local rockhounds.