Glowing Bone

"Mysterious beast bones that glow blue. There are currently no beasts alive with such bones and these seem to belong to an extinct beast species of long ago. The adventurer who first discovered these bones was ecstatic, believing them to be a form of ancient art. However, an appraiser told the adventurer that that was not the case and bought them for a pittance. Nowadays, they find use as a dye and so trade at a stable price despite having no discernible artistic value."