Minecraft wiki entry for Amethyst_Cluster, associated text: When mined without Silk Touch or broken by being pushed off an attached block by a piston or sticky piston, only fully grown amethyst clusters drop amethyst shards, while amethyst buds drop nothing. Breaking an amethyst cluster with a pickaxe drops 4 shards while any other method of breaking it yields 2 shards. The maximum amount of amethyst shards dropped can be increased with Fortune; Fortune I gives a 1⁄3 chance for 8 shards (averaging 5.33 shards), Fortune II gives a 25% chance (each) to give 8 or 12 shards (averaging 7 shards), and Fortune III gives a 20% chance (each) to give 8, 12, or 16 shards (averaging 8.8 shards). These are the same percentage increases as ores (except redstone ore and ancient debris).