You brought purple blocks home from a geode, arranged them carefully, and waited. Nothing grew. The likely problem is not the room’s decoration: an ordinary amethyst block is different from budding amethyst, the block that produces new crystals.
Before making another mining trip, separate the growing block, the crystal attached to it and the shards you want to collect. They are related items with different jobs.
Leave the X-marked blocks where you found them
Mojang’s amethyst explanation identifies budding amethyst by the X pattern on its surface. In ordinary Survival play, breaking it destroys it, even with Silk Touch; a piston does not provide a moving solution either. Ordinary amethyst blocks brought home are decorative, not replacements for that growth source.
When opening a geode, pause before clearing the purple layer. Identify the budding blocks first and choose a walking route that leaves them intact. The convenient block to remove for a doorway may be exactly the one you wanted to keep producing crystals.
Harvest the attachment, not its support
The Java release notes that introduced amethyst distinguish four stages: small, medium and large buds, followed by a full cluster. They also explain that growth happens on budding amethyst with an available face adjoining air or source water.
For a simple manual collection area, keep the crystal-bearing faces accessible and avoid enclosing them in decorative solid blocks. Aim at the protruding crystal when harvesting. Removing its supporting budding block trades a renewable source for an irreversible mistake.
Choose shards or a crystal decoration before swinging
A full cluster can provide shards when mined with an appropriate pickaxe, while Silk Touch collects the crystal form itself. Fortune is relevant when seeking more shard drops. Silk Touch on a cluster and Silk Touch on the budding block are therefore not equivalent actions.
Label or separate your tools before working in a cramped geode. If the result in your inventory is a crystal rather than loose shards, check which tool you used before assuming the world is broken. Do not experiment by breaking the growth source to see whether the enchantment behaves differently this time.
Make the return trip easier than the first discovery
Mark the entrance and record its location using the navigation options available in your edition or server. Put that information somewhere you will recognise later, including whether the entrance is above or below your usual path. A vague note such as “purple cave near home” becomes less useful after another evening of exploration.
On the next visit, inspect growth instead of expecting a fixed number of shards on a fixed schedule. Harvest mature clusters, preserve the budding blocks, and keep the route clear. The repeatable resource is the geode you can return to, not a pile of purple blocks in your house.
