Petrified Wood

Hardness: 6.5-7 (Mohs scale); Color: Highly variable, often brown, tan, red, green, black due to impurities like iron oxides, manganese, and carbon; Luster: Vitreous to waxy; Crystal structure: Cryptocrystalline to microcrystalline (quartz/chalcedony); Cleavage: None; Specific Gravity: 2.6-2.7

Formed when wood is buried under sediment and protected from decay by oxygen and organisms. Mineral-rich water flows through the sediment, replacing the original organic material of the wood with silica (typically chalcedony, a microcrystalline form of quartz). This permineralization process preserves the original cellular structure of the wood. The geological age can vary widely, from millions to hundreds of millions of years old, depending on the fossilized specimen. It commonly forms in volcanic ash beds or sedimentary deposits where rapid burial and silica-rich groundwater are present.

Prized as an ornamental stone and for collecting. Used in jewelry (cabochons, beads), decorative objects (bookends, tabletops, carved items), and as a landscape feature. Larger specimens are highly valued by collectors.

Petrified wood is a fossil in which the organic remains have been replaced by minerals in the slow process of permineralization. The cellular structure of the original wood is often perfectly preserved, allowing scientists to identify the species of trees that lived millions of years ago. The variation in color comes from the different minerals present during fossilization; for example, iron oxides create red and brown hues, while manganese can create black. The Petrified Forest National Park in Arizona is world-renowned for its vast deposits of colorful petrified wood.

In the field, petrified wood can be identified by its distinctive woody grain patterns, often exhibiting annual growth rings, bark textures, and knots, even though it feels and behaves like stone. It is typically found in areas with ancient volcanic activity or sedimentary basins. Look for areas with eroded volcanic ash layers or riverbeds. Its hardness and density distinguish it from modern wood. Common locations include the southwestern United States (Arizona, Utah, New Mexico), Madagascar, Argentina, and parts of China. For collectors, look for specimens with distinct wood grain, interesting colors, and an overall aesthetic appeal; cutting and polishing often reveal its internal beauty.