It’s Lapiz. It’s Lazuli. It’s Lapiz Lazuli!
Ok, now lapiz is a dye. There is no sole purpose for lapiz, except for dying things like leather armor, wool, and firework stars. Lapiz is fairly rare, and makes a good trick. Why? A solid Lapiz block looks a lot like water from a distance. Jump, and crack! Respawn, please. So lapiz has some uses, but not a lot of them.