Minecraft wiki entry for Fossils, associated text: The basic branch mining mechanics here are the same as layout 2 for the branch mining mentioned in Tutorials/Mining. However, the tunnels feeding off of the long tunnel should be 6 - 8 blocks from each other, which could also be said as having 5 - 7 blocks in between them. For the best overall efficiency, make the tunnels with 6 blocks in between them, or 7 blocks from each other. There is only one type of fossil that generates smaller than this. All other fossils are at least 5 blocks wide on every side, making them able to be seen in tunnels that have 6 blocks in between them. If you want to make sure you get every fossil, make your branch mine tunnels with 4 blocks in between, or 5 blocks from each other. However, although you will see every single fossil there is this way, it is inefficient.