I am missing the last (tenth) lava stone at the Egyptian level, too. I think I got the other 9 from the dragons I've defeated, but I need ten to get the last glyph to open the chest. Can't find the last one, though the island is not really large and quite open.
I can't continue playing, because there is nothing else to do on this level, and if I quit it, I will have to restart the level
Can anyone help me?