I was out working on Hunter achievements and saw this quest piece had nothing written on it so I decided to find out what it was for. Turning this in to Bellfast in Corathus Creep pops open the task window and gives the following text,
Bellfast says, 'Oh my! You say you found this near Stoneroot Falls? Let me look at into this.' With that the rusty old gnomework drops the gem fragment into his mouth. A moment later he pulls it back out and shakes his head. 'Nothing. There are no memories intact in it. But there's only one answer that makes sense. It was a shiliskin that picked up Fibblebrap's Fibblebrap gem in the mines and you found this on this Warlock Therigal. It must belong to Fibblebrap! You're a brave soul and you've already been into what's left of Illsalin. I don't suppose you could go back and search this Therigal's residence? He might have my friend.'
Perhaps this was the original intended method of starting the 2nd mission of the Fibblebrap arch?