Here's the fastest way to find diamonds in Minecraft. Click F3 to see your coordinates and then start digging down until you reach Y level 5. Now that you're Y5, mine re-blocks forward and then all the blocks you're right, all the blocks up, and all the blocks to your left. Repeat this until you find diamonds. Once you do find diamonds, go and mine them. But there's another secret. You have to do F3 and G to show chunk borders. Then you can mine without mining to any other sides until you find yellow lines. There can only be one diamond vein per chunk. So until you enter a different chunk, there's no point in looking for more diamonds.