Brian sent us this picture of his jewelry-mounted 5 franc coin from France. You can see in the picture that the gold coin has been soldered directly to the mounting hardware. This renders the coin of no value to coin collectors. They are such a finicky bunch! They will not stand for any type of damage to their coins. Even the scratch on Napoleon's face would be enough damage to turn most collectors totally off.
Since the coin is gold, all is not lost. The piece still has value. There is the intrinsic value of gold in the coin. The catalogs report 0.0467 troy ounces of gold in this coin. At the current gold 'spot' value (use kitco.com to find value today) of $1090 US dollars per troy ounce, the value computes to 0.0467 x 1090 = $51 per coin.
If you have a coin mounted as jewelry, take it to a jeweler for an in-person appraisal. It is not a collectible coin, so taking it to a coin dealer will yield a low price.