Petrified Wood

Hardness: 6.5–7 on Mohs scale. Color: Brown, tan, orange, and black (due to iron, manganese, and carbon). Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6–2.9.

Formed through permineralization, a process where organic material is replaced by silica (calcedony or opal) as groundwater permeates buried wood in sedimentary environments. Most specimens date from the Triassic to the Tertiary periods (20 to 200 million years ago).

Used in high-end lapidary work, jewelry, stone furniture (slabs), and interior design. It is highly valued as a collectible fossil specimen for education and display.

Petrified wood is the state fossil of Arizona. The process is so precise it can preserve microscopic cellular structures of the original tree, allowing paleobotanists to identify the specific mahogany or conifer species from millions of years ago.

Identify in the field by looking for bark-like textures on the exterior and characteristic growth rings or cellular structures on cross-sections. Commonly found in Arizona (Petrified Forest National Park), Oregon, Madagascar, and Indonesia. Collectors should look for 'rainbow' colors and well-defined knots.