Minecraft wiki entry for Things_not_to_do, associated text: If a player is mining, they should bring at least a few stone pickaxes with them, or the materials to make them and a crafting table. Mining stone with an iron pick is fast but consumes a lot of durability, and it is quite possible for the pick to break before diamonds (or any other precious mineral) is found. Note that this is not much of a problem when at lower y-levels, as it is likely to encounter more iron before your pickaxe breaks. If you have an iron farm or can get iron pickaxes from villager trading, feel free to ignore this, and use your iron pickaxes to mine stone.