The phrase 'Fool's Gold' is used when talking about an item that its owner believes to be valuable, but that really is not so.
Example of Use: “That investment seemed to be a good one, but I found out that it was fool’s gold when it crashed and burned.”
Interesting fact about Fool's Gold
Fool’s gold is a yellow mineral that can be mistaken for gold. When a less-than-knowledgeable miner stumbles upon what he believes to be the mother lode only to discover that the mineral is worthless, he has been said to have come upon fool’s gold.
