Arthur,
If they look like these:
[img:663:599]http://tmobilesimcards.files.wordpress.com/2007/08/663px-t-mobile_sim_card_front_and_back.jpg[/img]
They are SIM cards from cell phones. As seen in the photo they can be attached to a large piece of plastic the size of a credit card if new.
Used ones will most likely be detached from the card.
If new and attached to a card the extra plastic will affect the yields per pound figure.
Steve