Minecraft wiki entry for End_spike, associated text: If the End biome is used in the overworld, End spikes generates without bedrock and end crystals, only obsidian, with some of them containing iron bars. End spikes generate near coordinates 0,0. If the terrain is high enough, End spikes can generate buried or inside caverns but generates air blocks around and on top of it. If End biomes generate next to other biomes near 0,0 only some End spikes generate.