Hello Mr. Edge -- Sounds like you have a replica of a California fractional, small denomination gold piece with a face value of one half dollar. These coins were privately minted in round and octagonal shapes in response to the sharp lack of small coinage during the gold rush of mid-1800.
Genuine Cal Gold pieces today catalog anywhere from $150 US dollars to several $1000s of US dollars, depending on specific pattern and condition. The details of these pieces is too specialized and too complex for the CoinQuest forum, but numismatist Mike Reisbord has a good site on Cal Gold, and CalGoldOnline.com is the definitive meeting place for collectors and dealers. If you have just the slightest interest in these coins, we strongly urge you to visit one or both of these sites for detailed information.
With Mr. Edge's piece, the question is authenticity. If the word REPLICA appears on the coin as you describe, it most certainly is just that -- a replica of a genuine piece. Nice replica coins these days sell for a few 10s of dollars.
Even without the word REPLICA, there are plenty of counterfeit Cal Gold pieces around. The coin in our main picture is a fake. If you think you have a real one, you should have it certified by a respected service such as PCGS, NGC, or ICG. Look them up on the Internet.