The Wishbone will pulse faster and the noise will become higher-pitched as you get closer to the Silver. Once you're above it, dig down and start mining the Silver boulder with your Iron Pickaxe. You should probably switch out Wishbone for Megingjord once you've found the Silver, because - just like Copper, Tin, Bronze, and Iron - Silver is heavy and cannot be transported through portals. I'd recommend digging around the Silver Ore boulder before mining it, to ensure you don't miss any of this valuable resource. But be aware that floating Silver Ore doesn't collapse like Copper does. The Wishbone can also sense other secrets in different biomes. You can use it to find buried Muddy Scrap Piles in Swamps, or treasure under burial grounds in Meadows. It works in exactly the same way as it does for detecting Silver Ore.