Petrified Wood

Hardness of 6.5 to 7 on the Mohs scale due to quartz replacement; colors vary widely including brown, white, gray, yellow, and red depending on trace minerals like iron and manganese; vitreous to dull luster; amorphous to microcrystalline quartz crystal structure; no cleavage; specific gravity around 2.5 to 2.7.

Formed when fallen trees are rapidly buried in low-oxygen, sediment-rich environments such as volcanic ash or river floodplains, preventing decay. Over millions of years, groundwater rich in dissolved silica percolates through the organic material, replacing cell walls atom by atom with chalcedony, quartz, or opal. Geological age ranges from millions to hundreds of millions of years old.

Used primarily for ornamental purposes, decorative stone, high-end lapidary work, bookends, tabletops, jewelry, and as prized specimens for fossil and mineral collectors.

Petrified wood retains the original microscopic cellular structure of the ancient trees, allowing scientists to identify exact prehistoric plant species. Famous locations include the Petrified Forest National Park in Arizona.

Can be identified in the field by distinct wood grain textures, growth rings, and bark-like outer layers combined with an uncharacteristically heavy weight and rock-like hardness. Common in sedimentary layers worldwide, particularly in desert regions and volcanic formations.