I was flossing my teeth with one of those dental flossers and as I was flossing between my 2nd/3rd teeth on the bottom, the flosser just flicks part of my 2nd tooth and it flies across the room. I managed to retrieve it, and it looks like a part of a tooth for sure. I feel my tooth with my tongue, and there is a ditch on my 2nd tooth. In addition, in the tooth in my mouth that was chipped off, there is black things on it. I am guessing because of that, it made my tooth weak enough to chip this part off.

http://img824.imageshack.us/i/dscf0012o.jpg/
That is the picture of the tooth in my mouth

http://img210.imageshack.us/i/dscf0017g.jpg/
That is the picture of the tooth that has been chipped off.

I'm just confused about the black part, how that could have been caused in the middle of my tooth. And I want to know if this can be fixable and if it is an easy process to do by dentists.