Jill:
It may be a reaction from the glue used to secure the clear material to the cardboard. Since it's around the edges of the chip it could be that, over time, the chemical from the glue was absorbed into the edges of the chip. Hope that didn't happen to any others.

By the way, I know you're the resident Harrah's expert. The chip shown below is from Harrah's in New Orleans. Do you know if it's one of the first for this casino or is it a recent issue?

Thanks.