Answer:
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.
Walk on the living, they don't even mumble. Walk on the dead, they mutter and grumble.
In the land of the green glass door there are riddles but no answers, sheets but no blankets, and books but no words. Name something found in the land of the green glass door.
Dies half its life. Lives the rest. Dances without music. Breathes without breath.
A certain wizard resided in a city made from this gemstone.
I am rarely touched but often held. If you are smart you'll use me well. What am I?