To weigh that much it would have to be SIGNIFICANTLY thicker than a dime. I still think the color is from environmental damage, but I might be able to explain the high weight. In 1970 there were some dime and quarter errors made by punching dime blanks out of quarter thickness stock and quarters from dime thickness stock. (I don't remember if this happened in Philadelphia or Denver but I think it was Denver.) But even that wouldn't completely explain the weight because a dime struck on quarter stock would weigh between 3.1 and 3.1 grams. So to weigh between 3.4 and 4 grams this dime would have to be thicker than a quarter. Did some more calculations and a dime on half dollar thickness stock would do it. If it isn't as thick as a half dollar I would pretty much guarantee your scale is off.