What Am I Riddles

Question: There are several different kinds, but the one you pick doesn't do its job.

What is it?

Question: What is he that builds stronger than either the mason, the shipwright, or the carpenter?

Question: I can be used to build castles,
but I crumble in your hands.
I can help a man see,
and am found all around the lands.

What am I?

Question: I may be of the eye,
in order I am pie,
in my center there is a star,
I keep medics where they are.

What am I?

Question: I'm made up of 12 completely different letters but you can type me with just 1, what am I?