Shell buttons

[ohyourgod]

I bought a cute cotton cardigan from a thrift store and noticed when I got home that the buttons have a pearlescent finish on them. They look like they might be made from shells. Is there such thing as a synthetic shell button? How can I tell if these are real or fake? Google isn't being particularly helpful.

Here is a link to a picture of real shell buttons in case I'm not being clear.