Stones are rated for their
Stones are rated for their “measure of hardness” (MOH). The harder they are, the more likely they are to withstand high temperatures. Any of the places that you can purchase stones will likely also include information on MOH. You’ll probably find more resources on setting stones in metal clay, but it will include the MOH information and temps the stones can withstand.
One link is this:
I haven’t tried firing stones in glass, and as they say in the link above, “there’s always the risk of losing a natural gemstone” (during firing). Proceed only if you are willing to lose the stone.
EDIT: All that being said, the other risk you’ll have is the incompatibility between the materials. Everything in this universe expands and contracts at a different rate when heated (in glass, the COE — expansion coefficient). Differences in expansion rate between the glass and the gemstones may cause the piece to crack. But like I say, I haven’t tried.
Jester’s Baubles Fused Glass Designs