I'm just full of ideas today. What if caerulium came from the event that formed Yih's ring. I stated earlier that the ring was a captured asteroid whose orbit had decayed in the geologically recent past prior to the Kindling. In addition to forming the ring, much material rained down onto the surface, forming a belt of caerulium deposites along the equator. Since this was geologically recent, these deposits would be at or near the surface right smack dab in the yinrih's home range.

Caerulium can be cold worked and has a relatively low melting point, but isn't practical for making tools. Nevertheless, it serves as a tutorial of sorts for vulpithecine metallurgy.