Neodymium magnets

This rare-earth metal, neodymium is a strong magnet that is used for checking for non precious metals in precious jewelry. Silver, gold and platinum are not attracted to this magnet. Most metals however, are attracted by this magnet even if there is very small amount of them.

It's not completely foolproof, because there are some metals not attracted to the magnet, but they are rarely used in jewelry, another case, when you are checking clasps and they are weekly attracted to magnet, it's because there is tiny metal spring inside, even if it's gold or silver. But for a quick check if you have large amounts of jewelry this magnet is ideal tool.

Some safety advice - don't leave these magnets where small children or animals can get to them. They are dangerous if swallowed, especially more than one, they are strongly attracted to each-other. Exercise common sense in terms of safety.