Fossil

In Minecraft, fossils are rare skeletal structures composed of bone blocks, coal ore, or diamond ore. They randomly generate in desert, swamp, and mangrove swamp biomes. Each chunk has two attempts to generate a fossil within y-coordinates 0 to 320 or -63 to -8 underground, each with a 1/64 chance. Fossils have an equal chance to generate as any of the four variants of skull or four variants of spine. Fossils initially generate a pure-bone layer with a structure integrity of 0.9, meaning 10% of the bone blocks are removed and do not override original terrain blocks, leaving 90% bone blocks. Next, the ore layer generates with a structure integrity of 0.1, replacing 10% of the existing fossil with coal ore for fossils that generate above Y level 0, or deepslate diamond ore for fossils that generate below Y level -8. The locations of these ore blocks do not always correspond with the voids generated in the initial bone fossil, resulting in an incomplete structure. Nether fossils, found in soul sand valleys, are composed only of bone blocks and have no reduced integrity and contain no other minerals.