Fossil

A fossil is a rarely-occurring skeletal feature composed of bone blocks, coal ore, or diamond ore.

Generation
Fossils randomly generate only in desert, swamp and mangrove swamp biomes. Each chunk has two attempts within y-coordinates 0 to 320 or -63 to -8 underground to generate a fossil, each with a chance of $1/64$. They have an equal chance to generate as any of the four variants of skull or four variants of spine.

Fossils first generate the pure-bone layer with a structure integrity of 0.9, meaning 10% of the bone blocks are removed and will not override original terrian 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, so the resulting combination of both generations will usually result in an incomplete fossil structure composed of bone blocks and ores.

Structure
Naturally-generated fossils are composed of a mix of bone blocks and coal or diamond ores, as detailed above. They are made with the NBT structure block file format and have NBT files for each type of fossil located in the folder minecraft.jar/data/minecraft/structures/fossil.

There are 4 type of skulls and 4 type of spines.

ID




Trivia

 * Hidden in the structure NBT is data that credits ProfMobius with the creation of the fossils.