Too Obscure For You?
The sandruby was featured in Final Fantasy IV, the only thing that can cure the Desert Fever Rosa was afflicted with. It wasn’t until Square re-released FF IV that we found out that the sandruby light is what cures the woman. And here I thought that simple jewlery could cure deadly diseases.
Anyway, the point of Aerimus grabbing the sandruby is that when one of your party members tried to do the same thing (from the Antlion beast) in FF IV, the jaws snapped. The beast is certainly not tame, and getting the ruby with your bare hands is certainly not a good idea.
And cannons, as Secret of Mana would assure you, are incredibly powerful.