Have a look. I took it to a coin expert and he didn't know what it was. It almost looks like the copper is showing through at the front.
Actually, people find these quite often. Here's an older thread for reference: http://www.cointalk.com/t187395/ And of course, "plated" quarters bring a premium on eBay: http://www.ebay.com/itm/1999-2008-S...ins_US_Individual&hash=item460c3ffa02&afsrc=1
Ya I see people quick to expect they are plated- but how can one know for sure? It is perhaps still clad, just hidden. I think from what I remember it was significantly heavier. I don't remember for sure.