Petrified Wood Black Retrò natural semi-precious stone literally encloses elements of petrified wood. Petrified wood is a fossil formed when the vegetal material is buried under sediments and protected from contact with oxygen and other organisms. The characteristic and unique elements and patterns in these petrified slabs show the growth rings of the original tree. This natural stone, thanks to its unique and profound performance characteristics and esthetics, is excellent for the widest variety of design solutions.