Everyone is so complicated about the Onyx Stone.

The simple answer can be that those stones are added for lore reasons.
So for game purposes, everywhere you find an Onyx Stone where normally its not expected, it serves as a breadcrump, a hint that something or someone has to do biusiness with SHAR or its a hint that the mentioned Party of Shadowheart (all are dead by now, as she tells us) left some clues to follow.
Those Stones can also be somekind of special payment for Shar supporters, which maybe they can change at their temple for another reward.
Or its just the way like secret Handsigns like from Moles Thieveguild.
Stones to show someone is a supporter of Shar.

Theres so many possibilities to give meaning to those stones.
But games normaly do not think too much around corners, it must be something simple, easy to comprehend.

My best guess:
Onyx Stones = breadcrumbs leading to part of story, like parts of puzzlepieces in a bigger story

Last edited by TheHero; 16/04/22 02:17 PM.