They seem like ordinary RFID chips. (I want to make emphasis on "LOOKS LIKE", cause I cant tell for sure).
NFC operates on 13.56Mhz and those seem like ordinary RFID tags (125KHZ tags, with no memory)
I could be wrong since form factor, is not the only matter to identify them. They also could be an NFC tag not compatible with your phone, but they should come up saying "tag not compatible".
Have you tried: NFC tools, its a free app from the market, It could get some information out of it, if not: IT LOOKS like a regular RFID tag. (do you have the link for those tags, from where you bought them?)