Ivory Tower Wizard Janssen:
You haven't left yet? There isn't any time! Hurry. You need to destroy the fragments before the crusher explodes. Do you want to die clutching these fragments?
There's a Hidden Crusher made by the wizards of Ivory Tower on Cruma Tower: Underground Lv. 3. Find the crusher and destroy the Shining Mysterious Fragments. And as proof, collect 20 Normal Fragment Dust.
But it requires magic to destroy something, so it could self-destruct by consuming any residual magic left on it.
If the crusher is destroyed before all the fragments are, you'll need to find another one.