I think it would be good to have some individuality to the gemstones, but I think deviations in hue would be a better indicator. Etchings would mean that somebody had already labeled them, and since our characters are still trying to figure out how they work, etchings don't seem likely. Unless, of course, you want to use the "ancient civilization" plotline, but I think I'd rather leave it open-ended for now. And, yes, I like the idea of two teleport sapphires being in use making a portal. I can also imagine Telio taking special interest in such transportation magic.