French gold coins from this period follow two basic designs. This one has a crowned and draped shield on the reverse, while the other design has a wreath. For the wreath design, click to this CoinQuest page. For the draped shield design, keep reading!
As with any gold coin, we must first address the value due to gold content alone. Here are the stats:
20 francs: 0.1867 troy ounces gold
50 francs: 0.4667 ounces gold
100 francs: 0.9334 ounces gold
Note that the word 'troy' is understood when referring to precious metals.
To find the value due to gold content, multiply the numbers above by the current price of gold (it changes every day). You can find the current price at kitco.com. For instance, if the gold price is $1560 US dollars per troy ounce, a 50 franc coin would carry $1560 x 0.4667 = $728 US dollars of gold value.
The base gold value applies to every gold coin, even those that have been damaged by cleaning, scratching, or other forms of mutilation. But if you have a gold coin in good numismatic (coin collector) condition, there is additional value that should be added to the basic gold value. Here are some approximate numbers:
circulated: add $50 US dollars to gold value
fully uncirculated: add $100
circulated: add $100 US dollars to gold value
fully uncirculated: add $400
50 francs dated 1855BB and 1856BB, double the added value
circulated: add $200 US dollars to gold value
fully uncirculated: add $1000
100 francs dated 1856BB, double the added value
100 francs dated 1870A are very rare and catalog at $25000 in well preserved condition