It's a clicky update in Chardok. You have to clear all the way down to The Chardok Palace and have green/blue/red portal access. Once you get down to the palace you will notice it looks just like Kor-Sha zone in. The hingestone is up the left staircase in a room with 3 ^^^ Sarnak. It's sitting on the bookcase at 899, -21, 264 .
In order to rebuild the Eye of the Siren, Pietre needs the correct gems combination to place within it. He will need a fear-imbued coldstone. He believes experiments on fear imbues are being done in Sebilis. He will also need a firestone cooled in an elemental pond, and a hingestone. Pietre is unsure where to get the firestone or hingestone.
I need the firestone, the coldstone, and the hingestone that Pietre requires.
I need a firestone cooled in an elemental pool.
I have the elemental-cooled firestone.
I need a fear-imbued coldstone.
I have the fear-imbued coldstone.
I need a hingestone.
I have the hingestone.
I have the three stones.
I need to bring these stones to Pietre.
I need to return to Pietre.
I have spoken with Pietre.
I have brought the stones to Pietre.
I have found the three stones and brought them back to Pietre.