Layers are made from Cave Stone. Cave Stone is the most common block, and Crystal Stone currently gives the most coins per 1 block in the game. The NPC (non-playable character) quest giver is ObscureEntity. His quests are currently the most difficult.
Crystal Cavern is the only zone based inside a cave. It is decorated with pillars and glowing crystals of various colors. The portal is also made of pillars. Crystal Cavern's shop is shaped like a pickaxe and its sell area is a crashed minecart filled with gems. The path consists of brown planks/bricks and is lit by stone braziers.