Good Riddles

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

Question: You went into the forest and got me,
you sat down to find me,
you went home with me because you couldn't find me.

What am I?

Question: What is in the middle of the moon, At the end of an igloo And goes round in loops?

Question: You wait for it. It appears, cracks, stays for a moment, then disappears before your eyes.