(I don't actually want you to do this, merely know if it's possible...)

[rab] Could I name those individuals? YES, although it would be subjective as there's certainly no canonical list of them. Would they all fit into the "stance" box? I WOULD HAVE THOUGHT SO for most people's lists. An academic in the right field might be able to overflow the stance box, but most reasonably erudite people would probably name four or so names.

[Inkspot] Are the people fictional? NO, by and large.

[Raak] Precious stones? NO *sustained applause from the audience*
[CdM] The word "stone" IS on the card *mounting excitement from audience*
[Inkspot] Back to Greek and Roman times? YES
[rab] Arthurian connection? NOT THAT I'M AWARE OF
[CdM] Alchemists' stone? YES. The words on the card were "Philosopher's Stone", and I have to say I'm very upset that Tuj never popped up with his normal question! I got in a bit of a tizzy over the legend/myth questions. To my knowledge, the philosopher's stone doesn't appear in a particular myth or legend or in what is conventionally called mythology (i.e. of the Greek and Roman variety), but one could call it a mythical or legendary object, so a hard one to answer helpfully. * transmutes baton into finest gold and hands to CdM*

Global Warming? No.

Visible? Yes.
Human Construct? Yes.
Fictional? No, although there are a few connections to works of fiction.

Symbol? I think the most helpful answer is no.

Smoke? No. (Abstract?)
Mirrors? No. (Abstract?)
An action? No.
An emotion? No.
Does it involve all mankind? I'm not sure that it makes much sense to talk of this "involving people", but if you insist on an answer, I would say that it does not involve all mankind.

Metaphor? No.

Used as means of communication? While that is not its primary use, it can be used as a means of communication in certain circumstances.

An art form? No.

Invention? It is a human construct that was invented, but you wouldn't normally call it an invention.