Minecraft wiki entry for Experience, associated text: Experience orbs vary in value. The general worth of an orb is reflected by its size, with eleven possible sizes corresponding to specific values. The three smallest sizes are the most commonly encountered, as the majority of experience dropped by mobs and blocks is less than ten. Dense experience orbs, from values 17 and up, have orange "eyes" or "cores", and are less frequently encountered, most commonly from defeating the ender dragon, wither and other players, disenchanting objects on a grindstone, breaking spawners, and collecting items from high- traffic furnaces. For performance improvement, experience orbs can also merge to create higher level orbs.