Petrified Wood

Hardness: 6.5-7 (Mohs); Color: Tan, brown, gray; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None; Specific gravity: 2.6-2.9

Formed through permineralization, where organic wood material is replaced by minerals, typically silica (quartz), from groundwater. This process usually occurs in volcanic ash beds or sedimentary basins over millions of years, often dating from the Paleozoic to Cenozoic eras.

Used primarily for lapidary work, jewelry making, bookends, decorative table tops, and as a popular collector's specimen.

The Arizona Petrified Forest is the most famous location; though it looks like wood, it is entirely stone. It retains the cellular structure of the original tree, allowing scientists to identify ancient species.

Identify by wood-grain appearance, growth rings, and bark-like texture combined with a stone-like hardness that cannot be scratched by a steel knife. Common in the Western United States, Madagascar, and Indonesia.