Do I have a cubic zirconia or glass 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 glass 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.

If it is cubic zirconia, what do you think the price range would be? (pics coming)