Puzzle Sun-Stone Piece 1: Solve a candles puzzle on the left side of that room. In the center platform you will find a first fragment.
Puzzle Sun-Stone Piece 2: Taimurian Camp, you should solve a Totems/Statues puzzle and after that you will find here (where Zaar stand on picture) a piece of stone.
Puzzle Sun-Stone Piece 3: Dura'Tyr room, check the picture and a map there to find in which room exactly.
Puzzle Sun-Stone Piece 4: Placed in Ziggurat of the Sun, just change a mirror near the teleporter on that hole and you will get it.