This is a Sacagawea dollar coin in some sort of pendant frame. While I don't know anything about the frame, the coin itself is made up of 88.5% copper, 6% zinc, 3.5% manganese, 2% nickel. Hope this helps out a bit.
Actually after some research I believe the coin itself isn't real. Still a cool looking pendant but I don't believe it is a real coin. Here is a link to the same pendant.