Amethyst Cluster

Amethyst buds are the first three stages of growth of amethyst clusters, which grow on budding amethyst.

Amethyst clusters are the 4th and final growth stage of amethyst buds, which drop amethyst shards when mined.

Breaking
The amethyst cluster block itself in any of its growth stages (rather than its amethyst shard drops) can be obtained by mining it with an iron, diamond or netherite pickaxe with the Silk Touch enchantment. When mined using any other tool, it drops nothing.

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 4 amethyst shards, while amethyst buds drop nothing. 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.

Natural generation
Amethyst buds and clusters generate naturally as part of amethyst geodes on the sides of budding amethysts.

Budding amethyst
Every random tick there is a 20 % chance for a budding amethyst to spawn a small amethyst bud on any of its sides as long as the block being replaced with the small amethyst bud is air or a water source block.

Usage
An amethyst bud placed on a budding amethyst (rather than any other block) regardless whether it was placed by the player or spawned by the budding amethyst itself will grow overtime, going through three growth stages – small, medium, and large – before reaching its 4th and final growth stage as an amethyst cluster, which drops amethyst shards when mined.

Light
Small, medium and large amethyst buds give off a light level of 1, 2 and 4 respectively, while amethyst clusters give off a light level of 5.

Sound
Uniquely among other blocks an amethyst cluster in all its growth stages makes a quiet overlay sound when generally interacted with as well as its block breaking sound when hit with a projectile.

Trivia

 * Amethyst cluster is commonly mistaken as an "ore", However amethyst cluster is a mineral, not an ore.