The Arkenstone

The Arkenstone is a defunct Quest artifact diamond belonging to the Dwarf role, which existed in versions of SLASH'EM before NetHack 3.3.0 made race and role separate choices. When carried, it gave magic resistance and acted as a luckstone. When invoked, it granted object detection, as per the potion. It is also available as a patch to vanilla NetHack, available here. In patch form, it grants conflict and aggravate monster and is occasionally generated in the inventory of dwarf kings. A demon will ask you to bribe it with the Arkenstone instead of money if it is in your inventory.

Origin

The Arkenstone comes from the Tolkien universe. It is an important Dwarven artifact gem, featured in the book "The hobbit".