What Am I Riddles

Question: What lightens the light and darkens the dark?

Question: Something all men have,
but all men deny.
Man created it,
but no man can hold it.

What is it?

Question: You put me on a table and cut me, but you don't eat me.

What am I?

Question: Different lights make me strange,
for each one my size will change.

What am I?

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?