Thanks for writing to us.
The black flakes can be due to the casts in the urinary tract
which are usually associated with stone formation. In case the flecks are persistent then an earlier evaluation would be helpful in an early diagnosis.
I hope this information has been both informative and helpful for you. You can consult me again directly through my profile URL http://bit.ly/Dr-Praveen-Tayal
Dr. Praveen Tayal