Five of them can also be given to you if you talk to Daria in Nektulos Forest at ( -408, 2, -1262 ) /waypoint -408, 2, -1262.
Examine the scrying stones while standing near a ground-based rainbow found randomly around certain POIs strewn across the Shattered Lands. This action is called: scrying.
While scrying, you will occasionally win one or more Ancient Silver Coins as a reward. Other rewards include vendor items which you can sell to the scrying stone merchants, pieces of wearable armor, Training Tomes, or random undead to fight. Most of the rewards also give you the option of getting more scrying stones instead.