Amethyst Geode Finder
Edition
Version
Seed
Anywhere from Y -58 to Y 30. Each marker shows its geode's own Y, so you know how far to dig.
About one geode in ten never forms: the game skips it when part of it would hit water, lava or bedrock. Nothing can tell which ones in advance, Chunkbase included.
On Java Edition, type /seed in chat (it needs cheats on, or operator rights on a server). On Bedrock, open the world's settings: the seed is listed under Game.