The Scrying Stones of Chthon first appeared in Marvel Comics' "Doctor Voodoo: Avenger of the Supernatural Vol 1 #1" in 2009, and appeared in 3 issues of that series.
It has not been revealed if the stones were created by Chthon himself or others using his magic (Darkhold). Using the stones, the user can see the location of other beings including Hell Lords. You can also use them to influence those one observes. Through the stones others can transport themselves to your location (and likely vice versa).
Doctor Voodoo during his time as the Sorcerer Supreme used the Scrying Stones of Chthon to help him monitor extradimensional mystical threats to his home dimension. He used the Lost Spirits of Shuma-Gorath to guard the stones. Unfortunately for him, it was turned against him as Nightmare traveled through one of the stones to his location.