Do I have a cubic zirconia or gl gem?

I found a rather sizable gem on the sidewalk (about the size of a small pea) a few years ago, and it's been sitting in my drawer ever since. I can read text through it, so I know it's not a diamond (those are too cloudy to read through), but I can scratch gl with the pointed end. I called up my local jewelers and they said appraisals are about 75 dollars, which I don't want to spend on something that I'm just curious about. Any input? I think it's a Brilliant cut.