Rare-earth elements

From having just watched TED-Ed’s YouTube video entitled “What’s a smartphone made of?” (lesson by Kim Preshoff) I gather with fascination that a smartphone’s components include rare-earth elements that may be uneconomical to mine in areas where they occur in low concentrations.



“A rare-earth element (REE) or rare-earth metal (REM), as defined by IUPAC, is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium,” Wikipedia.

According to the Wikipedia article:

Despite their name, rare-earth elements are – with the exception of the radioactive promethium – relatively plentiful in Earth's crust, with cerium being the 25th most abundant element at 68 parts per million, more abundant than copper.

Hence the importance of hyphens in spelling. In the phrase rare-earth element, the hyphen makes it clear that the adjective “rare” does not apply to the noun “element”.