Lore:
“ 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
An option to use them as a handheld torch would be useful and lore friendly, with no repair cost, just a slightly longer repair time perhaps for balance issues.
You can use them as a torch, and you can also dye the colour of light, by putting a dye in the torchs inventory ~
How do you use them then? Why I try to equip the stone it just says “This item cannot be moved”
Not a handheld torch, unfortunately. It would be cool. But you can craft standing torches with them as of right now! 
I second this, witchfire and radium gems as hand torches would be nice, would need to be a lot brighter and last a good while longer given the cost to make them however compared to the existing hand torches.
Awesome idea, though maybe having the radium torch have an unlimited lifetime since it’s expensive to craft and considered a magical item iirc.