Are there any antecedents other than Tolkien for trolls turning to stone?
When I was a kid, I remember trolls appearing in one of the earliest episodes of The Real Ghostbusters (the fifth episode "Troll Bridge"), the plot is resolved by having one of the trolls apparently* turned to stone after being shot with the Ghostbusters' proton packs.
As a kid, familiar with The Hobbit, this seemed like perfectly logical outcome for a troll bombarded by highly energetic particles. The episode also invoked classic elements of troll folklore, particularly in having a group of trolls emerge from under a bridge to occupy the span.
Years later, it occurred to me that I was not familiar with any older folklore tradition of trolls turning to stone. My own feeling of familiarity with the notion came entirely from Tolkien. So is The Hobbit really the original source for trolls that turn to stone (under whatever circumstances)?
*In fact, the stone troll was a fake—a garden statuette modified to fool the other trolls. So it was actually left unclear what would have happened if the Ghostbusters had shot one of the trolls.