Being a 1991, I'd say 1 cent value. As for the looks, Could be lots of different things, use, abuse, ground effects? I believe it is copper coated zinc.
Yep,the date will tell you everything,along with a good coin book. Mineralization in the ground,water,fertilizer,etc. can alter the looks of a coin,no matter what it's made of.
Good luck out there!
Queation I have, is how did you come by it? If its a dug coin, it's probably just environmentally damaged. If it came out of circulation, it is a possibility that you have a coin missing its copper coating. If that's the case, it might be a mint error and have some value. If it's environmentally damaged, just spend it. Check it out with someone who knows mint errors to get some insight.