Petrified Wood

Hardness: 6.5-7 (Mohs scale); Color: Brown, tan, black, and grey; Luster: Waxy to dull; Crystal structure: Amorphous to microcrystalline (cryptocrystalline quartz); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.9.

Formed through permineralization where organic remains (trees or tree-like plants) are replaced by minerals, usually silica (quartz or chalcedony), as water rich in dissolved minerals seeps through sediment. This process typically occurs over millions of years (often Mesozoic or Cenozoic eras) in anaerobic environments like volcanic ash or river floodplains.

Used primarily for display specimens, lapidary work (jewelry, beads, cabochons), furniture (table tops), and landscaping. It is highly valued by fossil and mineral collectors.

Petrified wood is the state fossil of Arizona, Mississippi, and Washington. Famous locations include the Petrified Forest National Park in Arizona, where massive logs of Araucarioxylon arizonicum are preserved in the Chinle Formation.

Identify in the field by looking for stone that retains the external texture of bark or internal growth rings. It is often heavier than regular wood and harder than steel. Commonly found in areas with past volcanic activity or ancient riverbeds.