Check the listing for details. Petrified Wood Tree Knot Approx. 8 Inch Specimen Slice. Condition: Used. Listed at 69.99 USD. This product is an approximately 8-inch specimen slice of petrified wood tree knot. Petrified wood is the result of wood turning into stone over millions of years due to the process of wood turning into limestone. This unique piece showcases the intricate details of a tree knot, making it a fascinating collectible for those interested in fossils, rocks, and minerals. It is a one-of-a-kind item that would make a great addition to any collection or display.