Answer:
Though blind as well, can lead the blind well.
He has one and a person has two. A citizen has three. And a human being has four. A personality has five. And an inhabitant of earth has six.
A certain wizard resided in a city made from this gemstone.
The man who invented it doesn't want it. The man who bought it doesn't need it. The man who needs it doesn't know it. What is it?
My first half is normally made of stone, my second is crazy, and I taste sweet when complete.
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.