Hi Carla --
Brighman Young himself was the architect behind a coinage system in Salt Lake City. Very few gold pieces in denominations from 2.5 dollars to 20 dollars were minted with dates 1849 and 1850. These coins are extremely rare, worth tens to hundreds of thousands of US dollars.
If your coin looks like my picture, it is a replica of the real thing and worth essentially zero, maybe a few dollars. Numismatist Mike Locke has a terrific web site on these old gold coins, and related coins and tokens, and you can learn a lot just browsing his web site. Thanks to Mike for letting CoinQuest use his image. Here is what he says about this piece:
I know of 5 different replicas of this coin, two of which are very accurate copies by C.M. Larson, including a pure gold version. The C.M. Larson replicas are edge marked C.M. Larson. The brass replicas weigh about 8 grams. The gold replica weighs 15.62 grams. The 2 cast pot metal replicas weigh 6 and 12 grams respectively. The correct weight for this piece is 14.3 grams, according to Don Kagin.
A picture of a genuine Mormon gold coin is found at CoinFacts. You can see the difference between the copy pictured and the real thing.
On the outside chance that you have a genuine piece or one of the gold replicas, you must take immediate steps to preserve it. The most important step is to never, never clean your coin. Write to us, or to Mike Locke, or to CoinFacts, for further instructions if you feel your piece is genuine.
Thanks for an interesting inquiry.