Sorry to hear that.
Oh well, we've all had those moments.
I had dug so many good looking rings with fake stones on them that it almost cost me my best ring ever. One day I was land hunting with a friend who happens to be a gold smith (repairs jewelry and such). I wandered up the side of a mowed grass hill and noticed some dirt erosion due to rain run off. I always eye spots like that by eye to see if anything has been exposed, not to mention hunt it because it gives you a little more depth having some dirt washed away.
I noticed a glint of gold by eye sticking out of the dirt! I could see what looked like the bottom of a ring's band sticking out of the soil. I called my friend up to watch me remove it. Pulled it out and flipped it over and looking up at us was a huge diamond set between two white gold lions on a yellow thick man's ring! My friend took it, looked close, and said "Don't get your hopes up. That stone looks odd for some reason." Besides all that, it looked like the band was flaking off like it was plated. Haven't been burned it seems like all the time before with my ring finds, I stuck it in my pouch and didn't think much of it.
Later, it started to rain, so he said let's go back to my shop and I'll test it for you on my diamond tester. On the ride there, still not having pretty much any hope at all, I started to pick at the flaking on the bottom part of the band. Hmmm....It's not exposing a base metal. After further inspection we found it was something that had rotted away and must have been used to tighten the ring up on the man's finger. Slightly more hope, but still that diamond looked to big, and as I said my friend who should know said it didn't look right.
Anyway, back at his shop, I was mindlessly staring at various equipment in the room when I heard "Sh*%!" That brought me out of my day dreaming and I looked over at him. He was constantly testing the stone to make sure the readings were right. This thing was testing real! Excited, he said for me not to get my hopes up yet, because that diamond tester doesn't seem to like him and he's had false positives with it before. So he called his partner up and he came out to further inspect it. Not only was it real, but after he convinced me to let him cut it out of the ring it turned out to be a high quality 2 carat diamond of excellent clarity!
The reason why it looked odd was it turns out it was an old miner's cut I think they called it from the 1800's. That was by far the best day of my hunting career, and I didn't even find it with my detector, I saw it by eye! Had I not seen it I doubt I would have detected and dug it, because that exposed ground was loaded with round tabs, and being a somewhat bigger ring, I think it probably would have read right in the higher pull tab range just like a lot of round tabs.
Had I not had my friend's expertise, and had I not more closely looked at the flaking on it, I might have thrown that ring into my junk box and never thought about it again, instead of it being given it's proper place and distinction among my "best finds".