Much much tougher brain teaser

[PorscheNGuns]

Most OOTers are probably not smart enough to figure this one out on their own, but nonetheless, don't spoil it if you know it.

You have 12 rocks and a scale, and 11 of the rocks weigh exactly the same. The remaining rock is either heavier or lighter than the other 11.

Using the scale only 3 times, figure out which one of the rocks is the odd one out, and whether it is heavier or lighter.

You only get one chance, I am holding a .357 mag to your head, and if you screw up, I blow your brains out. Go!

-Matt