Gold. Think about it, there isn't much use for it really. There's no point wasting your gold on tools, swords and armor. How many clocks do you need when you can just look at the sun. And if you need gold nuggets to make potions, all it takes is one gold ingot and you already have nine.
Do you wish there were better things to do with your gold? Or maybe if you could exchange it for something else? Now there's a block that makes gold worth mining. It's called the Lucky Block, and can be crafted with 4 gold ingots and a dropper, and can also be found naturally in your world. When you mine this block it will have an equal chance of dropping items, spawning entities or structures.
WARNING: If luck is not on your side, this block may have devastating effects on you or your world. It is recommended that you backup your world, use a not important world or go hardcore and take the risk.