Petrified Wood

Hardness: 6.5-7 (Mohs scale), Color: Brown, tan, reddish, grey, Luster: Vitreous to waxy, Structure: Cryptocrystalline quartz (Chalcedony), Cleavage: None/Conchoidal fracture

Formed when plant material is buried by sediment and protected from decay by oxygen and organisms. Groundwater rich in dissolved solids flows through the sediment, replacing the original plant material with silica, calcite, or pyrite. Found in geological formations ranging from the Devonian to the Holocene.

Used in jewelry (cabochons), interior design (tables, bookends), ornamental carvings, and as a popular educational specimen for geology collectors.

Petrified wood allows scientists to study ancient ecosystems. Some of the world's most famous deposits are in the Petrified Forest National Park in Arizona, where 225-million-year-old trees were preserved.

Identify in the field by checking for wood-grain patterns, bark textures, or growth rings on a stone that is much harder than wood and cold to the touch. Commonly found in areas with past volcanic activity that provided silica-rich ash beds.