Petrified Wood

Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including brown, tan, black, red, yellow, and white due to mineral impurities. Luster: Vitreous to waxy when polished, dull when raw. Crystal structure: Cryptocrystalline (quartz/chalcedony replacing organic material). Cleavage: None (conchoidal fracture). Specific gravity: 2.5 to 2.7.

Formed when ancient trees or plants are rapidly buried in low-oxygen, sediment-rich environments such as river floodplains or volcanic ash beds. Over millions of years, groundwater rich in dissolved silica (quartz) percolates through the organic tissue, replacing the original cellulose and lignin molecule by molecule with minerals while preserving the detailed cellular structure. Most petrified wood dates from the Triassic to Tertiary periods (ranging from 50 to over 200 million years ago).

Used primarily in lapidary arts for making decorative objects, bookends, spheres, cabochons for jewelry, and as high-demand display specimens for fossil and mineral collectors.

Famous localities include the Petrified Forest National Park in Arizona, USA, and the petrified forests of Madagascar and Argentina. Despite looking like stone, petrified wood is actually a fossilized record of ancient forests.

Can be identified in the field by its distinct tree-bark texture, growth rings, or wood grain combined with an unusually high weight, cold feel, and a Mohs hardness that easily scratches glass. Common worldwide wherever ancient terrestrial sedimentary layers are exposed.