I have a couple of cobbles made from the same material and am not an expert on tools. I would say it could go either way. Someone will come along and let you know their opinions but I would have picked it up and brought it back too and even though I've been told mine are just cobbles with the exception of one of them which was more than likely a mano, something has told me to keep them separate from the rest of the quartz cobbles, maybe because that material is rare for me to find, or it could be that I've seen discoidals in my area made from the same material. Have you found any projectile points or pottery where you found it?