Silver Coins are a very unusual type of PoE Orb. They cannot be used directly at all, but you may obtain Prophecies by spending Silver Coins. Some of the end-game Prophecies can be extremely expensive, with The Queen's Sacrifice being the most expensive of them all. It can be used to obtain Atziri's Reflection, which is one of the most expensive Uniques in Path of Exile. If you want to grind Prophecies, you may want to buy Silver Coins on Odealo from other players. You can find cheap offers on Silver Coins with fast delivery times, posted by reliable sellers. Trading on Odealo is possible on all the platforms: PC, Xbox One, and PS4.