[...]unless you have changed it so that we need something other than a shell to make a staff with a different element.
If that were the case, you would have needed at least 3 components to make any staff to begin with. Having fire as the default element for 2 components and requiring additional components to make any other element doesn't make sense. Not to mention, if nothing else, the shells are more water-related than fire.
That said, at this point we might as well just pray that the next Divinity game will have a group of devs who actually sit down and focus on designing a real, proper crafting system that has a bit of depth and is fun to play with.