Does mica in shampoo damage hair?

I think I read somewhere a long time ago that the mica that is found in some shampoos and conditioners (evidently put in to make the hair shiny) can damage the hair -- weaken it, cause breakage, or some such. Has anyone else read whether this is true?

I just accidentally bought some shampoo with mica in it (well, I meant to buy the shampoo -- just didn't realize that it had mica in it!), and am trying to decide whether to return it.