The Arkenstone of Thrain
A great globe seemingly filled with moonlight, the famed Heart of the
Mountain, which splinters the light that falls upon it into a thousand
glowing shards.
It can be activated for detection every 30+d30 turns if it is being
worn. It provides light (radius 3) forever. It increases your speed
and luck by 3. It provides resistance to life draining, light, dark
and chaos. It allows you to see invisible monsters. It allows you
to sense the presence of orcs. It cannot be harmed by acid, cold,
lightning or fire.
Level 50, Rarity 50, 0.5 lbs, 50000 Gold

(T.o.M.E. 2.3.5)