Black flakes in hot water pipe

For some time I have noticed an increasing amount of black flakes exiting with the hot water in my bathroom sink. The flakes swim on the water surface. They are very thin and tend to disintegrate when I touch them. When I try to wipe them from the surface of the sink, they become e 'smear' which takes a household cleaner to remove. After some running the tap water gets clean and stays that way for a day or two. The problem occurs only in the two sinks of one bathroom, not the other bathrooms nor in the jacuzzi of the same bathroom. Any idea what those black flakes might be and how to get rid of the problem would be much appreciated.
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For some time I have noticed an increasing amount of black flakes exiting with the tap water in two bathroom sinks. The flakes swim on the surface of the water in the sink. When I touch them, they tend to disintegrate; when I try to wipe them off the surface of the sink, they 'smear' and it takes a household cleaner to remove that smear. After some time of running the hot water the water becomes clean an it stays that way for a day or two. The problem occurs only in one bathroom, not in the others, nor in the kitchen, nor in the Jacuzzi of that same bathroom. Any ideas as to what those flakes are and how to get rid of the problem would be much appreciated.
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I found by watching the Si-Fi Channel those are very dangerous Aliens. Your hand will now fall off.
Its your washer or ' O' ring disintegrating if its *black and it leaves a black rubber smudge mark on your fingers.

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kitchen,
flakes
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