Minecraft wiki entry for Budding_Amethyst, associated text: Budding amethyst produces amethyst clusters using a mechanic similar to cocoa pod growth. Each time budding amethyst receives a random tick, there is a 20% chance of creating amethyst clusters on any side which is covered only by air or water. If there is already an amethyst bud on that particular side, the bud instead reaches its next growth stage.