In The Hobbit...

[Raefindel]

This is from The Tolkien Companion ;

...Yet one memory has lingered with espeical clarity: the association of the Troll-race with stone, the substance of their being. Trolls bore thesame relationship to stone as Ents did to wood; of stone they were made in theri beginning, and to stone they returned if caught by the direct rays of the noonday Sun; for like the Orcs they were bred during the years of the Great Darkness of the First Age, and so the Sun was their enemy...

So it seems that everyone's guesses were very educated guesses. [img]smilies/cool.gif[/img]