I was playing singleplayer, Normal difficulty, and found an amethyst geode at -58y. Mining with iron pickaxe or diamond pickaxe did not allow for the blocks of amethyst to drop.

I have played on a server that allowed for them to drop with iron. I have taken a video with creative attained blocks to show the blocks wouldn't drop and that it wasn't due to y level.

Seed is -8171583380010173648

Version is 21w11a - Singleplayer

Windows, Java edition