"Rare-earth elements" is a name for a set of particular elements. Cobalt is not among them. Despite their name rare-earth elements are not that rare either. Th

"Rare-earth elements" is a name for a set of particular elements. Cobalt is not among them. Despite their name rare-earth elements are not that rare either. They occur in rather low concentrations though and never pure either (i.e. always as compounds) which makes mining and processing them complex. https://en.wikipedia.org/wiki/Rare-earth_element https://en.wikipedia.org/wiki/Rare-earth_element