What is this mysterious black matter found on my teeth?

[Jay520]

So for the past few months, whenever I look in the mirror, I occasionally find some black stuff on my teeth. It looks like the outer layer of some sort of peanut shell. But that's the problem, I have not eaten any peanuts in a long time. I usually just remove the stuff off my teeth with no harm done but I'm still concerned. What is this stuff and what is doing there?

I'm pretty sure it has nothing to do with my hygiene because I brush my teeth when needed. I also watch what I put in mouth, so it shouldn't be some external entity. But I'm still genuinely concerned since I'm sure this isn't a common occurrence. Anyone ever experience this phenomenon? If so, what did you do?

This really has been affecting me mentally because I'm always wondering if my mouth is dirty or not when I talk to people, so I'm willing to do anything you guys say as long as it's within reason.

I hope I don't have some sort of health concern. If so, then I hope it's contagious, because I'd like to infect others with my issue.

Thanks, and Happy Thanksgiving Eve!