It's called petrified wood.
Petrified wood is formed when a mineral called silica is deposited in pores of dead tree trunk.
Petrified wood is preserved when water seeps into the tissue of the tree trunk and the wood hardens to a rock. The dissolved silica takes the place of wood that has rotted away One of the most well known petrified forests is in Eastern Arizona. It was established as a national monument in 1906 and as a national park in 1962. Petrified wood has a structure that is something like this. It includes bark, growth rings and rock.