You've got an interesting coin, Huey. It is from Switzerland, not France, but these two countries have a lot in common from a numismatic (coin collector) point of view. Both have coins with denominations sol, centime, and franc.
Your coin is from the days of the Swiss Cantons, the early states comprising the Swiss Federation. Specifically it is from the Canton of Geneva (Geneve). The inscription Post Tenebras Lux means 'Light After Darkness' which originates in the Bible (Job 17:12) and was adopted by Christian leaders and also by the city of Geneva.
There were 12 deniers in a sol, so UN SOL 6 D indicates one and one-half sol.
These coins were minted in billon (an alloy of silver and copper) and in silver. Huey states his coin is made of gold, but this is very improbable. Perhaps Huey's coin is gold plated, which will lower value substantially. Or perhaps it has picked up a spiffy golden toning, which will increase value substantially!
NEVER CLEAN A COIN. CLEANING RUINS VALUE.
The coin catalogs list these coins with decent value, and you can find the around the Internet for sale a good prices. The coin in our picture comes from respected eBay seller AspenCoins where it sold retail for $28 US dollars. A dealer might pay $10 to $14 for this coin, keeping the dealership afloat by selling it at twice that amount.
Dates range from 1817 to 1833 and there are minor variations in the patterns. In general all these coins, the 6D, UN SOL, and US SOL 6D, as well as all the dates, carry prices that about the same, as follows:
COINS MINTED IN BILLON:
worn: $5 US dollars approximate catalog value
average circulated: $10
well preserved: $25
fully uncirculated: $75
COINS MINTED IN SILVER:
worn: $10 US dollars approximate catalog value
average circulated: $25
well preserved: $75
fully uncirculated: $150
Remember to use the principles described on our Terminology page to convert these inflated catalog values to actual buy and sell values.