Impurities in flour

I have noticed lately, in my flour, teeny tiny bits of black. We think it's a flaking off of the machinery used to mill the flour..it is not a bug.

I have noticed it when kneading for quite awhile and couldn't figure out the source. A few weeks ago I sifted through my bag of robin hood whole wheat flour and deduced that's where it's coming from.  I've contacted them and sent a small sample to see if they can tell me what it is. I decided to buy my whole wheat at my local bulk barn and was surprised to see, if I look very closely, the small black bits in the spelt and the rye flours....possibly others, but I didn't want to attract attention :)

I'm sure it's not harmful but I've googled and can see no other reference. I saw the black bits and pointed it out to my husband so I know I'm not crazy..in the bulk barn we were both looking in the bins and pointing out the bits...so I wonder....has anyone else noticed it? It's not in the whites..only in the 'whole grain' types...