Mineral/Fossil (Sedimentary context)

Petrified Wood

Silicified Wood (SiO2 - primarily Quartz/Chalcedony/Opal)

Hardness: 6.5–7 on Mohs scale. Color: Brown, tan, reddish-orange to black. Luster: Waxy to vitreous (glassy). Crystal Structure: Microcrystalline (Cryptocrystalline). Cleavage: None (conchoidal fracture). It is heavy for its size due to high silica content.

Hardness: 6
Color: Brown, tan, reddish-orange to black
Luster: Waxy to vitreous (glassy)

Identified March 2, 2026More mineral/fossil (sedimentary context) →

Explore Petrified Wood in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed via permineralization, where organic wood material is replaced by minerals (usually silica) from groundwater while buried under sediment or volcanic ash. This typically occurs over millions of years, often dating back to the Triassic or Jurassic periods.

Uses & applications

Used in high-end furniture (slabs), jewelry (cabochons), interior design (bookends, sculptures), and highly sought after by geological collectors for display.

Geological facts

Famous locations include the Petrified Forest National Park in Arizona. In some cases, the replacement is so perfect that the original cellular structure and tree rings of the wood are visible under a microscope despite the wood being entirely stone.

Field identification & locations

Identify in the field by looking for bark-like textures or growth rings on stones that feel significantly harder and smoother than surrounding rocks. Common in arid desert regions or areas with ancient volcanic activity.

Other mineral/fossil (sedimentary context) specimens

See all

Ferruginous Sandstone Concretion (Ironstone Phosphorite)

Ferruginous Sandstone (variable Fe-oxide/hydroxide composition)

sedimentary

Sandstone Concretion

Limonitic Sandstone Concretion

sedimentary

Sandstone Concretion

Ferruginous Sandstone Concretion (Primarily SiO2 with Iron Oxide cement)

sedimentary

Ironstone Concretion

Limonitic/Hematitic Concretion

sedimentary

Chert (with Drusy Quartz Pocket)

Silicon Dioxide (SiO2)

sedimentary

Limestone

Calcium Carbonate (CaCO3)

sedimentary