Where And When Did Riddle Learn About .cruxes

There is no mention In any books in Hogwarts? <_<

We may find out in book 7, unless it really isn't that important.

I believe it to be very important.......This means someone was teaching Tom to become Immortal, Who, and why?

also can a .crux be made unknowingly? I don't think so. So their is no way for Harry to be a .crux. Because Voldy didn't know he was going to be defeated. ( G.O.F. in the graveyard ) . Plus He was there to kill Harry why would he want to kill him If his..(Voldy's) soul was to reside in Harry?

Unless tom happened to come across the name of horcruxes in a book and he knew it was dark magic because of the book he saw the name in. Or he could have overheard some dark wizards talking about horcruxes

Hermione, Ron and Harry do find a reference to it in Magick Moste Evile, which was in the Restricted Section - but it merely says, "Of the Horcrux we will not speak." As Hermione (I think) says, why even mention it? But it sounded like Tom Riddle at least had a vague idea as to what they were when he asked Slughorn about them... he obviously knew that they were something that could enhance immortality, which was what he wanted.