Fossilized Wood (Petrified Wood)

Hardness: 6.5-7 on Mohs scale (due to quartz replacement); Color: Highly variable, often browns, tans, grays, black, red, and blue due to mineral impurities (iron oxides, manganese, copper); Luster: Dull to waxy; Crystal structure: Cryptocrystalline to microcrystalline (quartz/chalcedony); Cleavage: None (fractures conchoidally); Specific gravity: 2.6-2.7

Formed when wood is buried by sediment or volcanic ash, protecting it from decay. Groundwater rich in dissolved silica (often from volcanic ash) flows through the sediment, replacing the organic material of the wood cell by cell with silica, preserving the original structure. Other minerals like iron, manganese, and copper can color the silica. Geological age varies widely, from millions to hundreds of millions of years, depending on the fossil occurrence.

Predominantly used for ornamental purposes, including polished slabs, carvings, cabochons, and beads for jewelry. Larger pieces are used in landscaping, as decorative objects, and for tabletops. It is also of significant interest to fossil collectors and paleontologists for studying ancient flora.

The fossilization process often preserves minute details of the original wood, including tree rings and cellular structures. Arizona's Petrified Forest National Park is one of the most famous localities for petrified wood, where vast forests were fossilized during the Late Triassic period. Some of the largest and most colorful examples come from this region. The unique coloration depends on the specific minerals present during silicification.

In the field, look for distinct wood grain patterns, annual rings, and often bark textures that are preserved in stone. It feels heavy for its size due to the mineral replacement and is hard enough to scratch glass. It often has a waxy or dull luster, and colors are typically earthy tones, though vibrant reds, blues, and yellows can occur. Commonly found in areas with past volcanic activity or sedimentary basins where rapid burial of forests occurred, such as deserts and riverbeds. Good indicators include areas with exposed ancient lake beds or ashfall deposits. Collectors look for pieces with well-preserved detail and vibrant colors.