About 4 weeks ago, I got chafed on the back of my heel, slightly above the edge of the shoe. I had tucked my pants into my socks and worn a second pair of pants on top of that, and that caused too much friction, thus the chafing. A scab formed, just a small injury, no big deal. Just about 1/2 inch long and less than 1/4 inch wide.

I did not put any cream on it, as it was so minimal, covered it with a band-aid for a few days, and then just let it heal. Which this thing stubbornly refuses to do. After 4 weeks, the scab is still there, adhering tightly, it does not come off, or heal up properly.

Anyone any suggestions as to why? Isn't 4 weeks a bit long for such a minor "injury"?

The socks that I wear on my runs do not chafe, and there has not been any further chafing since, and nothing (except socks) touches the area during the day. I wear boots only occasionally, and they don't rub or chafe, either. I am clueless.

Yep, I've had scabs for a long time, too.  Especially where skin is thicker/tougher like on my feet.  I agree with warden - If it is not infected, it should be fine.

I agree.  As long as there is no infection I wouldn't worry.  It might be deeper that you thought or the scab may just be hanging on while the skin underneath is already healed.  In either case, just leave it alone.