Is the coin thinner than a normal dime? If so, someone with too much time on their hands probably smoothed it off with a file or other tool. If not, you could have an error coin that results when two blanks (called planchets) fall into the coin press at the same time. One planchet is struck with the front image and the other with the reverse-side image, but the two sides of the planchets that were facing each other don't receive an image from the dies. I'm not an expert on all error coins so I can't provide a value. You'd need to take the coin to a dealer or coin show and have it evaluated by someone who specializes in errors.