On the topic of Trolls turning into stone, we only have one actual description of it actually happening, as far as I know.
Quote:
"Dawn take you all, and be stone to you!" said a voice that sounded like William's. But it wasn't. For just at that moment the light came over the hill, and there was a mighty twitter in the branches. William never spoke for he stood turned to stone as he stooped; and Bert and Tom were stuck like rocks as they looked at him. And there they stand to this day, all alone, unless the birds perch on them; for trolls, as you probably know, must be underground before dawn, or they go back to the stuff of the mountains they are made of, and never move again. That is what had happened to Bert and Tom and William.
The Hobbit, Roast MuttonFor this passage we can conclude that trolls turn into stone by daylight. From the first emphasized part, it isn't clear whether it was direct sunlight, or just daylight that 'hit' them, but from the seconds emphasized part, it is clear that it is just the light of day (from what I can make of it, to be exact: direct or indirect light of the sun between dawn and sunset).
Now it is interesting to wonder what happens if Frodo's troll would have stepped into the daylight of the Chamber of Mazarbul. Would he have been petrified as he was 'hit' by the light of day, or would he have remained alive as he was underground (which they have to be to remain alive, according to this passage)...
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, there was 1 Troll or maybe more, Gandalf wasn't sure:
