Yours vs. your's

Which is correct “Is that yours?” or “Is that your’s?”?

I ask because it is possessive, so I would think it would be the latter, but I typically use and see the former usage.

Are there particular cases in which one should be used instead of the other? Or is one simply correct and the other not?

This is one of the few things that still confuse me, so help is greatly appreciated.

It would definitely, unequivocally, and undeniably be yours. Same with ours. No apostrophe needed, and if you put one in, dark things may happen.

From NOAD:

yours |yôrz; yoŏrz| possessive pronoun

1 used to refer to a thing or things belonging to or associated with the person or people that the speaker is addressing : the choice is yours | it's no business of yours.