Not sure if you have found a 2000 $1 Mule coin?
These coins were struck with the reverse of a $1 coin but the obverse of a 10 cent piece.
Easy to identify because the dies of a 10 cent coin are slightly smaller than the collar of a $1 coin. When the coin is pressed, the gap between the collar and the die creates an outer rim. These appear as a pair of concentric circles about the rim on the obverse.
Don’t confuse this double rim with a similar effect that is caused by a minor misstrike in which the coin was struck slightly off-center. The double rim caused by a minor misstrike only circumscribes a portion of the coin, meaning the double rim effect might appear around the left-hand side of the coin but not around the right, or vice versa. On a mule dollar, the double-rim effect traces the entire circumference of the coin.