Petrified wood is a type of fossil formed when trees or wood are buried under sediment and mineral-rich water. Over time, the organic material in the wood is replaced by minerals, such as silica, calcite, or pyrite, turning it into stone while preserving the original structure of the wood. This process can take millions of years. The result is a beautiful, colorful stone that often displays the tree's growth rings and bark patterns. Petrified wood can be found in various locations around the world, with notable sites including the Petrified Forest National Park in Arizona. It is often used for decorative purposes and as a collector's item.