I think that's the one that's kinda nearby where the pit is in the big windy desert. *It's supposed to glow to help you figure out which one you need to bring to him. *I haven't played in a long while... *Can you be more specific?
Yeah,*it's mission 17. Listen to what TigerC10 said and then go to the big stone mountain. It's northeast from the center of the big windy desert. If you go around the stone mountain, you should find it(it will be glowing like TigerC10 said.).