The Stone of Lore
A great emerald that fills your mind with images of knowledge and dreadful
understanding as you stare into its depths.
It can be activated for perilous identify every turn if it is being
worn. It provides light (radius 1) forever. It cannot be harmed by
acid, cold, lightning or fire.
Level 15, Rarity 12, 1.5 lbs, 20000 Gold

(T.o.M.E. 2.3.5)