Recover The Star Sapphire - NWN Side Quest (Chapter 3)
Recover the Star Sapphire is a side quest that begins by speaking with Husher Clay inside of the Trading Post building in Beorunna's Well. For this quest you'll be tasked with visiting Layenne's Tomb in the second (northern) Coldwood map and solving the puzzle in that tomb to claim the gem.
The puzzle that you need to solve in Layenne's Tomb is pretty straight forward. You'll have to collect 4 different gems from inside of the tomb and place them into the correct pedestals to make the Star Sapphire appear. The 4 gems you need are the Gem of Pain, Gem of Honor, Gem of Misery and Gem of Duty. I've included a screenshot below that shows you the map locations of all 4 of these gems.
As you could probably already guess, I strongly recommend you clear out this entire tomb while doing this quest. There is a lot of loot to find here and a lot of enemies for EXP waiting for you.
When you are ready to finish this quest and get your hands on the Star Sapphire item you'll want to go to the southern Pedestal Room which is marked on my map above. In this room you will find 5 regular pedestals that you can interact with. The one in the middle won't have anything on it but the 4 surrounding pedestals will all have a tablet in their inventory.
So, how this works is you need to place the Gems you collected into the correct pedestal. Once you fill up all 4 pedestals with the right gems you will be able to collect the Star Sapphire out of the middle pedestal. Below you'll find a quick list detailing which Gem goes into which pedestal.
Tablet of Purple Light: Gem of Misery
Tablet of Green Light: Gem of Duty
Tablet of White Light: Gem of Honor
Tablet of Blue Light: Gem of Pain
Putting the correct gem into the pedestal will make a light appear above it. Using the wrong gem will give you an error "The gem is rejected." Once you've put all 4 gems into their correct places a light will also appear above the central pedestal and you'll be able to collect the Star Sapphire.
All that's left now is to return to Beorunna's Well and give the Star Sapphire to Husher Clay inside of the Trading Post.