What is the black mold on carrots?

One day I went out to eat and my carrots looked black. It didn't look like mold, but i wasn't sure so I didn't eat them. Later, at home a took a carrot and placed it over a match it formed a black ring just like the one in the restaurant. So, if you ever have a carrot with a black ring in it is from a fire or it is sometimes mold.