Dora has brought us an interesting piece. It is a replica of a US Goloid Dollar. If it were real, it would be worth several thousands of US dollars. The replica is worth a few dollars. Values for genuine coins are tucked away in coin catalogs and range from $2500 to $10000 US dollars. You can find a picture of the genuine coin at CoinAucstionsHelp. The nice-looking genuine coin at HeritageAuctions sold for $3700.
The first test of authenticity should be weight. If your coin weighs 14.25 grams, it may be real. If it does not weigh 14.25 grams, it is fake. Most of the coins you see today are fakes.
Now, according to those Smarty Pants over at Answerbag:
'Goloid is an alloy of silver, gold and copper patented by Dr. William Wheeler Hubbell on May 22, 1877. The alloy, in varying proportions (sometimes slightly out of these specifications), was used by the United States Mint to strike pattern dollars, sometimes called 'metric dollars' (some were marked with 'metric' in the coin design, while all had metal proportions and total coin weight as design features) from 1878 to 1880. Patterns of the same design were struck in other metals, including aluminum, copper, normal coin silver, lead, and white metal.
In the end, goloid was rejected as a coinage metal because it could not be distinguished from the normal U.S. 90% silver coin alloy without chemical analysis, thus inviting counterfeiters to use silver-copper alloys alone to make lower-value copies.'