Idea for a crystal cave.

Kind of an amalgamation of an amethyst geodes and stalagmites/stalactites. Create a rare cave system that has large crystals of varying colours sizes and shaped that look like stalagmites/stalactites. When broken with a silk touch pickaxe you should get an item that can be crafted into an iridescent crystal block which changes colour slightly based on light and the perspective of the player. For a better example of what I mean search "quartz cave" on your  nearest browser and head to images you should see super large crystals in a cave system. Or you could look at the picture of one that I attached. Obviously it does not need to be this complicated that would be very tricky to pull off.