With the cave update coming up, I figured this would be a good time to post this here. I hope you enjoy!
Caves are known for many things, one of which are crystals. As another cool feature for the caves of Minecraft, I created a new cave biome where huge crystals spawn, akin to the Cave of the Crystals, an actual place in Mexico.
This new biome contains pillars stretching from the cave ceiling to the floor and from wall to wall and sticking out in all directions, composed of new blocks called Mirfractite Columns, and different blocks for smaller columns and for the tops of larger ones.
(A crystal that sticks up and stops, and a horizontal column.)
The shorter blocks on top of the big pillars are called Mirfractite columns, and spawn in their own shorter pillars. The very smallest block is called a crystal cap, and spawns at the top of the pillars.
When mined without silk touch, the blocks will drop a few Mirfractite Shards. These can be crafted into Mirfractite bricks, 2 possible variants of which I've designed here. These can be made into slabs, stairs, and walls. There's also smooth and chiseled versions to build with.
One of the biggest reasons to seek out the Mirfractite is a new redstone block: the Sensor. This handy block is crafted with Mirfractite Shards and detects the light level in front of it, sending out a light signal opposite to that in strength. This could make for some cool puzzles, like a room in a temple that detects when someone places a torch via a Sensor hidden behind a slab, or another way to make a light that turns off during the daytime.
Top to bottom: Mirfractite Shards, 2 brick concepts, Chiseled and Smooth Mirfractite, and the back and front of the Sensor.
Mirfractite Shards can be found in stronghold hallway chests and in dungeons.
I had a similar thought regarding giant crystal caves, only the mineral would be gypsum, which could be used to craft drywall, basically like carpet for walls so that the inside and outside of a building with a one block thick wall could be different colors/textures. Such caves would be rare and very deep and waterlogged. To be useful for survival, as long as the caves remained waterlogged, the crystals could keep growing, becoming a renewable resource.