Radium Gem

Description
"'They are jewels, fused with radium. You rub them with your thumb to make them glow, and rub them again, the opposite way, to extinguish them.'"

- Xuthal of the Dusk

The product of a science long vanished in the ancient past, these gems seem to glow indefinitely when activated. There is a cost, however, as those who use the Radium Gems seem to slowly lose their grip on sanity, whispering to themselves of green stoned cities and the nameless horrors that stalk them.